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docs: scheduler: convert docs to ReST and rename to *.rst
In order to prepare to add them to the Kernel API book, convert the files to ReST format. The conversion is actually: - add blank lines and identation in order to identify paragraphs; - fix tables markups; - add some lists markups; - mark literal blocks; - adjust title markups. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mauro Carvalho Chehab
Jonathan Corbet
parent
d223884089
commit
d6a3b24762
@ -11,4 +11,4 @@ Description:
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example would be, if User A has shares = 1024 and user
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B has shares = 2048, User B will get twice the CPU
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bandwidth user A will. For more details refer
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Documentation/scheduler/sched-design-CFS.txt
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Documentation/scheduler/sched-design-CFS.rst
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@ -1,3 +1,4 @@
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================================================
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Completions - "wait for completion" barrier APIs
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================================================
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@ -46,7 +47,7 @@ it has to wait for it.
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To use completions you need to #include <linux/completion.h> and
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create a static or dynamic variable of type 'struct completion',
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which has only two fields:
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which has only two fields::
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struct completion {
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unsigned int done;
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@ -57,7 +58,7 @@ This provides the ->wait waitqueue to place tasks on for waiting (if any), and
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the ->done completion flag for indicating whether it's completed or not.
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Completions should be named to refer to the event that is being synchronized on.
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A good example is:
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A good example is::
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wait_for_completion(&early_console_added);
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@ -81,7 +82,7 @@ have taken place, even if these wait functions return prematurely due to a timeo
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or a signal triggering.
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Initializing of dynamically allocated completion objects is done via a call to
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init_completion():
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init_completion()::
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init_completion(&dynamic_object->done);
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@ -100,7 +101,8 @@ but be aware of other races.
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For static declaration and initialization, macros are available.
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For static (or global) declarations in file scope you can use DECLARE_COMPLETION():
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For static (or global) declarations in file scope you can use
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DECLARE_COMPLETION()::
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static DECLARE_COMPLETION(setup_done);
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DECLARE_COMPLETION(setup_done);
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@ -111,7 +113,7 @@ initialized to 'not done' and doesn't require an init_completion() call.
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When a completion is declared as a local variable within a function,
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then the initialization should always use DECLARE_COMPLETION_ONSTACK()
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explicitly, not just to make lockdep happy, but also to make it clear
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that limited scope had been considered and is intentional:
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that limited scope had been considered and is intentional::
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DECLARE_COMPLETION_ONSTACK(setup_done)
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@ -140,11 +142,11 @@ Waiting for completions:
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------------------------
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For a thread to wait for some concurrent activity to finish, it
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calls wait_for_completion() on the initialized completion structure:
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calls wait_for_completion() on the initialized completion structure::
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void wait_for_completion(struct completion *done)
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A typical usage scenario is:
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A typical usage scenario is::
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CPU#1 CPU#2
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@ -192,17 +194,17 @@ A common problem that occurs is to have unclean assignment of return types,
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so take care to assign return-values to variables of the proper type.
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Checking for the specific meaning of return values also has been found
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to be quite inaccurate, e.g. constructs like:
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to be quite inaccurate, e.g. constructs like::
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if (!wait_for_completion_interruptible_timeout(...))
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... would execute the same code path for successful completion and for the
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interrupted case - which is probably not what you want.
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interrupted case - which is probably not what you want::
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int wait_for_completion_interruptible(struct completion *done)
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This function marks the task TASK_INTERRUPTIBLE while it is waiting.
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If a signal was received while waiting it will return -ERESTARTSYS; 0 otherwise.
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If a signal was received while waiting it will return -ERESTARTSYS; 0 otherwise::
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unsigned long wait_for_completion_timeout(struct completion *done, unsigned long timeout)
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@ -214,7 +216,7 @@ Timeouts are preferably calculated with msecs_to_jiffies() or usecs_to_jiffies()
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to make the code largely HZ-invariant.
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If the returned timeout value is deliberately ignored a comment should probably explain
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why (e.g. see drivers/mfd/wm8350-core.c wm8350_read_auxadc()).
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why (e.g. see drivers/mfd/wm8350-core.c wm8350_read_auxadc())::
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long wait_for_completion_interruptible_timeout(struct completion *done, unsigned long timeout)
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@ -225,14 +227,14 @@ jiffies if completion occurred.
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Further variants include _killable which uses TASK_KILLABLE as the
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designated tasks state and will return -ERESTARTSYS if it is interrupted,
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or 0 if completion was achieved. There is a _timeout variant as well:
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or 0 if completion was achieved. There is a _timeout variant as well::
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long wait_for_completion_killable(struct completion *done)
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long wait_for_completion_killable_timeout(struct completion *done, unsigned long timeout)
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The _io variants wait_for_completion_io() behave the same as the non-_io
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variants, except for accounting waiting time as 'waiting on IO', which has
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an impact on how the task is accounted in scheduling/IO stats:
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an impact on how the task is accounted in scheduling/IO stats::
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void wait_for_completion_io(struct completion *done)
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unsigned long wait_for_completion_io_timeout(struct completion *done, unsigned long timeout)
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@ -243,11 +245,11 @@ Signaling completions:
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A thread that wants to signal that the conditions for continuation have been
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achieved calls complete() to signal exactly one of the waiters that it can
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continue:
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continue::
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void complete(struct completion *done)
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... or calls complete_all() to signal all current and future waiters:
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... or calls complete_all() to signal all current and future waiters::
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void complete_all(struct completion *done)
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@ -276,14 +278,14 @@ try_wait_for_completion()/completion_done():
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The try_wait_for_completion() function will not put the thread on the wait
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queue but rather returns false if it would need to enqueue (block) the thread,
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else it consumes one posted completion and returns true.
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else it consumes one posted completion and returns true::
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bool try_wait_for_completion(struct completion *done)
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Finally, to check the state of a completion without changing it in any way,
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call completion_done(), which returns false if there are no posted
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completions that were not yet consumed by waiters (implying that there are
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waiters) and true otherwise;
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waiters) and true otherwise::
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bool completion_done(struct completion *done)
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29
Documentation/scheduler/index.rst
Normal file
29
Documentation/scheduler/index.rst
Normal file
@ -0,0 +1,29 @@
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:orphan:
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===============
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Linux Scheduler
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===============
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.. toctree::
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:maxdepth: 1
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completion
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sched-arch
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sched-bwc
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sched-deadline
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sched-design-CFS
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sched-domains
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sched-energy
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sched-nice-design
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sched-rt-group
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sched-stats
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text_files
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.. only:: subproject and html
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Indices
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=======
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* :ref:`genindex`
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@ -1,4 +1,6 @@
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=================================================================
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CPU Scheduler implementation hints for architecture specific code
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=================================================================
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Nick Piggin, 2005
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@ -35,9 +37,10 @@ Your cpu_idle routines need to obey the following rules:
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4. The only time interrupts need to be disabled when checking
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need_resched is if we are about to sleep the processor until
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the next interrupt (this doesn't provide any protection of
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need_resched, it prevents losing an interrupt).
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need_resched, it prevents losing an interrupt):
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4a. Common problem with this type of sleep appears to be::
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4a. Common problem with this type of sleep appears to be:
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local_irq_disable();
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if (!need_resched()) {
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local_irq_enable();
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@ -51,7 +54,7 @@ Your cpu_idle routines need to obey the following rules:
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although it may be reasonable to do some background work or enter
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a low CPU priority.
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5a. If TIF_POLLING_NRFLAG is set, and we do decide to enter
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- 5a. If TIF_POLLING_NRFLAG is set, and we do decide to enter
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an interrupt sleep, it needs to be cleared then a memory
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barrier issued (followed by a test of need_resched with
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interrupts disabled, as explained in 3).
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@ -71,4 +74,3 @@ sh64 - Is sleeping racy vs interrupts? (See #4a)
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sparc - IRQs on at this point(?), change local_irq_save to _disable.
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- TODO: needs secondary CPUs to disable preempt (See #1)
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@ -1,8 +1,9 @@
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=====================
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CFS Bandwidth Control
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=====================
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[ This document only discusses CPU bandwidth control for SCHED_NORMAL.
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The SCHED_RT case is covered in Documentation/scheduler/sched-rt-group.txt ]
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The SCHED_RT case is covered in Documentation/scheduler/sched-rt-group.rst ]
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CFS bandwidth control is a CONFIG_FAIR_GROUP_SCHED extension which allows the
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specification of the maximum CPU bandwidth available to a group or hierarchy.
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@ -27,7 +28,8 @@ cpu.cfs_quota_us: the total available run-time within a period (in microseconds)
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cpu.cfs_period_us: the length of a period (in microseconds)
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cpu.stat: exports throttling statistics [explained further below]
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The default values are:
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The default values are::
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cpu.cfs_period_us=100ms
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cpu.cfs_quota=-1
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@ -55,7 +57,8 @@ For efficiency run-time is transferred between the global pool and CPU local
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on large systems. The amount transferred each time such an update is required
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is described as the "slice".
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This is tunable via procfs:
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This is tunable via procfs::
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/proc/sys/kernel/sched_cfs_bandwidth_slice_us (default=5ms)
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Larger slice values will reduce transfer overheads, while smaller values allow
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@ -66,6 +69,7 @@ Statistics
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A group's bandwidth statistics are exported via 3 fields in cpu.stat.
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cpu.stat:
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- nr_periods: Number of enforcement intervals that have elapsed.
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- nr_throttled: Number of times the group has been throttled/limited.
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- throttled_time: The total time duration (in nanoseconds) for which entities
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@ -78,12 +82,15 @@ Hierarchical considerations
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The interface enforces that an individual entity's bandwidth is always
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attainable, that is: max(c_i) <= C. However, over-subscription in the
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aggregate case is explicitly allowed to enable work-conserving semantics
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within a hierarchy.
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within a hierarchy:
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e.g. \Sum (c_i) may exceed C
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[ Where C is the parent's bandwidth, and c_i its children ]
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There are two ways in which a group may become throttled:
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a. it fully consumes its own quota within a period
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b. a parent's quota is fully consumed within its period
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@ -92,7 +99,7 @@ be allowed to until the parent's runtime is refreshed.
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Examples
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--------
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1. Limit a group to 1 CPU worth of runtime.
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1. Limit a group to 1 CPU worth of runtime::
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If period is 250ms and quota is also 250ms, the group will get
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1 CPU worth of runtime every 250ms.
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@ -100,10 +107,10 @@ Examples
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# echo 250000 > cpu.cfs_quota_us /* quota = 250ms */
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# echo 250000 > cpu.cfs_period_us /* period = 250ms */
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2. Limit a group to 2 CPUs worth of runtime on a multi-CPU machine.
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2. Limit a group to 2 CPUs worth of runtime on a multi-CPU machine
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With 500ms period and 1000ms quota, the group can get 2 CPUs worth of
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runtime every 500ms.
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runtime every 500ms::
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# echo 1000000 > cpu.cfs_quota_us /* quota = 1000ms */
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# echo 500000 > cpu.cfs_period_us /* period = 500ms */
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@ -112,11 +119,10 @@ Examples
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3. Limit a group to 20% of 1 CPU.
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With 50ms period, 10ms quota will be equivalent to 20% of 1 CPU.
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With 50ms period, 10ms quota will be equivalent to 20% of 1 CPU::
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# echo 10000 > cpu.cfs_quota_us /* quota = 10ms */
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# echo 50000 > cpu.cfs_period_us /* period = 50ms */
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By using a small period here we are ensuring a consistent latency
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response at the expense of burst capacity.
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@ -1,8 +1,8 @@
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========================
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Deadline Task Scheduling
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------------------------
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========================
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CONTENTS
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========
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.. CONTENTS
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0. WARNING
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1. Overview
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@ -44,7 +44,7 @@ CONTENTS
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2. Scheduling algorithm
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==================
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=======================
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2.1 Main algorithm
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------------------
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@ -80,7 +80,7 @@ CONTENTS
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a "remaining runtime". These two parameters are initially set to 0;
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- When a SCHED_DEADLINE task wakes up (becomes ready for execution),
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the scheduler checks if
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the scheduler checks if::
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remaining runtime runtime
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---------------------------------- > ---------
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@ -97,7 +97,7 @@ CONTENTS
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left unchanged;
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- When a SCHED_DEADLINE task executes for an amount of time t, its
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remaining runtime is decreased as
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remaining runtime is decreased as::
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remaining runtime = remaining runtime - t
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@ -112,7 +112,7 @@ CONTENTS
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- When the current time is equal to the replenishment time of a
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throttled task, the scheduling deadline and the remaining runtime are
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updated as
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updated as::
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scheduling deadline = scheduling deadline + period
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remaining runtime = remaining runtime + runtime
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@ -129,7 +129,7 @@ CONTENTS
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Reclamation of Unused Bandwidth) algorithm [15, 16, 17] and it is enabled
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when flag SCHED_FLAG_RECLAIM is set.
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The following diagram illustrates the state names for tasks handled by GRUB:
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The following diagram illustrates the state names for tasks handled by GRUB::
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------------
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(d) | Active |
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@ -168,7 +168,7 @@ CONTENTS
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breaking the real-time guarantees.
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The 0-lag time for a task entering the ActiveNonContending state is
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computed as
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computed as::
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(runtime * dl_period)
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deadline - ---------------------
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@ -222,7 +222,7 @@ CONTENTS
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Let's now see a trivial example of two deadline tasks with runtime equal
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to 4 and period equal to 8 (i.e., bandwidth equal to 0.5):
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to 4 and period equal to 8 (i.e., bandwidth equal to 0.5)::
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A Task T1
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|
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@ -284,7 +284,7 @@ CONTENTS
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2.3 Energy-aware scheduling
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------------------------
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---------------------------
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When cpufreq's schedutil governor is selected, SCHED_DEADLINE implements the
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GRUB-PA [19] algorithm, reducing the CPU operating frequency to the minimum
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@ -299,15 +299,20 @@ CONTENTS
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3. Scheduling Real-Time Tasks
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=============================
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* BIG FAT WARNING ******************************************************
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*
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* This section contains a (not-thorough) summary on classical deadline
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* scheduling theory, and how it applies to SCHED_DEADLINE.
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* The reader can "safely" skip to Section 4 if only interested in seeing
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* how the scheduling policy can be used. Anyway, we strongly recommend
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* to come back here and continue reading (once the urge for testing is
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* satisfied :P) to be sure of fully understanding all technical details.
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************************************************************************
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.. BIG FAT WARNING ******************************************************
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.. warning::
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This section contains a (not-thorough) summary on classical deadline
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scheduling theory, and how it applies to SCHED_DEADLINE.
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The reader can "safely" skip to Section 4 if only interested in seeing
|
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how the scheduling policy can be used. Anyway, we strongly recommend
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to come back here and continue reading (once the urge for testing is
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satisfied :P) to be sure of fully understanding all technical details.
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.. ************************************************************************
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There are no limitations on what kind of task can exploit this new
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scheduling discipline, even if it must be said that it is particularly
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@ -329,6 +334,7 @@ CONTENTS
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sporadic with minimum inter-arrival time P is r_{j+1} >= r_j + P. Finally,
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d_j = r_j + D, where D is the task's relative deadline.
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Summing up, a real-time task can be described as
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Task = (WCET, D, P)
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The utilization of a real-time task is defined as the ratio between its
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@ -352,13 +358,15 @@ CONTENTS
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between the finishing time of a job and its absolute deadline).
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More precisely, it can be proven that using a global EDF scheduler the
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maximum tardiness of each task is smaller or equal than
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((M − 1) · WCET_max − WCET_min)/(M − (M − 2) · U_max) + WCET_max
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where WCET_max = max{WCET_i} is the maximum WCET, WCET_min=min{WCET_i}
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is the minimum WCET, and U_max = max{WCET_i/P_i} is the maximum
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utilization[12].
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3.2 Schedulability Analysis for Uniprocessor Systems
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------------------------
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----------------------------------------------------
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If M=1 (uniprocessor system), or in case of partitioned scheduling (each
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real-time task is statically assigned to one and only one CPU), it is
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@ -370,7 +378,9 @@ CONTENTS
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a task as WCET_i/min{D_i,P_i}, and EDF is able to respect all the deadlines
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of all the tasks running on a CPU if the sum of the densities of the tasks
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running on such a CPU is smaller or equal than 1:
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sum(WCET_i / min{D_i, P_i}) <= 1
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It is important to notice that this condition is only sufficient, and not
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necessary: there are task sets that are schedulable, but do not respect the
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condition. For example, consider the task set {Task_1,Task_2} composed by
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@ -379,7 +389,9 @@ CONTENTS
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(Task_1 is scheduled as soon as it is released, and finishes just in time
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to respect its deadline; Task_2 is scheduled immediately after Task_1, hence
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its response time cannot be larger than 50ms + 10ms = 60ms) even if
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|
||||
50 / min{50,100} + 10 / min{100, 100} = 50 / 50 + 10 / 100 = 1.1
|
||||
|
||||
Of course it is possible to test the exact schedulability of tasks with
|
||||
D_i != P_i (checking a condition that is both sufficient and necessary),
|
||||
but this cannot be done by comparing the total utilization or density with
|
||||
@ -399,7 +411,7 @@ CONTENTS
|
||||
4 Linux uses an admission test based on the tasks' utilizations.
|
||||
|
||||
3.3 Schedulability Analysis for Multiprocessor Systems
|
||||
------------------------
|
||||
------------------------------------------------------
|
||||
|
||||
On multiprocessor systems with global EDF scheduling (non partitioned
|
||||
systems), a sufficient test for schedulability can not be based on the
|
||||
@ -428,7 +440,9 @@ CONTENTS
|
||||
between total utilization (or density) and a fixed constant. If all tasks
|
||||
have D_i = P_i, a sufficient schedulability condition can be expressed in
|
||||
a simple way:
|
||||
|
||||
sum(WCET_i / P_i) <= M - (M - 1) · U_max
|
||||
|
||||
where U_max = max{WCET_i / P_i}[10]. Notice that for U_max = 1,
|
||||
M - (M - 1) · U_max becomes M - M + 1 = 1 and this schedulability condition
|
||||
just confirms the Dhall's effect. A more complete survey of the literature
|
||||
@ -447,7 +461,7 @@ CONTENTS
|
||||
the tasks are limited.
|
||||
|
||||
3.4 Relationship with SCHED_DEADLINE Parameters
|
||||
------------------------
|
||||
-----------------------------------------------
|
||||
|
||||
Finally, it is important to understand the relationship between the
|
||||
SCHED_DEADLINE scheduling parameters described in Section 2 (runtime,
|
||||
@ -473,6 +487,7 @@ CONTENTS
|
||||
this task, as it is not possible to respect its temporal constraints.
|
||||
|
||||
References:
|
||||
|
||||
1 - C. L. Liu and J. W. Layland. Scheduling algorithms for multiprogram-
|
||||
ming in a hard-real-time environment. Journal of the Association for
|
||||
Computing Machinery, 20(1), 1973.
|
||||
@ -550,7 +565,7 @@ CONTENTS
|
||||
The interface used to control the CPU bandwidth that can be allocated
|
||||
to -deadline tasks is similar to the one already used for -rt
|
||||
tasks with real-time group scheduling (a.k.a. RT-throttling - see
|
||||
Documentation/scheduler/sched-rt-group.txt), and is based on readable/
|
||||
Documentation/scheduler/sched-rt-group.rst), and is based on readable/
|
||||
writable control files located in procfs (for system wide settings).
|
||||
Notice that per-group settings (controlled through cgroupfs) are still not
|
||||
defined for -deadline tasks, because more discussion is needed in order to
|
||||
@ -596,11 +611,13 @@ CONTENTS
|
||||
Specifying a periodic/sporadic task that executes for a given amount of
|
||||
runtime at each instance, and that is scheduled according to the urgency of
|
||||
its own timing constraints needs, in general, a way of declaring:
|
||||
|
||||
- a (maximum/typical) instance execution time,
|
||||
- a minimum interval between consecutive instances,
|
||||
- a time constraint by which each instance must be completed.
|
||||
|
||||
Therefore:
|
||||
|
||||
* a new struct sched_attr, containing all the necessary fields is
|
||||
provided;
|
||||
* the new scheduling related syscalls that manipulate it, i.e.,
|
||||
@ -658,7 +675,7 @@ CONTENTS
|
||||
------------------------------------
|
||||
|
||||
An example of a simple configuration (pin a -deadline task to CPU0)
|
||||
follows (rt-app is used to create a -deadline task).
|
||||
follows (rt-app is used to create a -deadline task)::
|
||||
|
||||
mkdir /dev/cpuset
|
||||
mount -t cgroup -o cpuset cpuset /dev/cpuset
|
||||
@ -671,8 +688,8 @@ CONTENTS
|
||||
echo 1 > cpu0/cpuset.cpu_exclusive
|
||||
echo 1 > cpu0/cpuset.mem_exclusive
|
||||
echo $$ > cpu0/tasks
|
||||
rt-app -t 100000:10000:d:0 -D5 (it is now actually superfluous to specify
|
||||
task affinity)
|
||||
rt-app -t 100000:10000:d:0 -D5 # it is now actually superfluous to specify
|
||||
# task affinity
|
||||
|
||||
6. Future plans
|
||||
===============
|
||||
@ -711,7 +728,7 @@ Appendix A. Test suite
|
||||
rt-app is available at: https://github.com/scheduler-tools/rt-app.
|
||||
|
||||
Thread parameters can be specified from the command line, with something like
|
||||
this:
|
||||
this::
|
||||
|
||||
# rt-app -t 100000:10000:d -t 150000:20000:f:10 -D5
|
||||
|
||||
@ -721,27 +738,27 @@ Appendix A. Test suite
|
||||
of 5 seconds.
|
||||
|
||||
More interestingly, configurations can be described with a json file that
|
||||
can be passed as input to rt-app with something like this:
|
||||
can be passed as input to rt-app with something like this::
|
||||
|
||||
# rt-app my_config.json
|
||||
|
||||
The parameters that can be specified with the second method are a superset
|
||||
of the command line options. Please refer to rt-app documentation for more
|
||||
details (<rt-app-sources>/doc/*.json).
|
||||
details (`<rt-app-sources>/doc/*.json`).
|
||||
|
||||
The second testing application is a modification of schedtool, called
|
||||
schedtool-dl, which can be used to setup SCHED_DEADLINE parameters for a
|
||||
certain pid/application. schedtool-dl is available at:
|
||||
https://github.com/scheduler-tools/schedtool-dl.git.
|
||||
|
||||
The usage is straightforward:
|
||||
The usage is straightforward::
|
||||
|
||||
# schedtool -E -t 10000000:100000000 -e ./my_cpuhog_app
|
||||
|
||||
With this, my_cpuhog_app is put to run inside a SCHED_DEADLINE reservation
|
||||
of 10ms every 100ms (note that parameters are expressed in microseconds).
|
||||
You can also use schedtool to create a reservation for an already running
|
||||
application, given that you know its pid:
|
||||
application, given that you know its pid::
|
||||
|
||||
# schedtool -E -t 10000000:100000000 my_app_pid
|
||||
|
||||
@ -750,7 +767,7 @@ Appendix B. Minimal main()
|
||||
|
||||
We provide in what follows a simple (ugly) self-contained code snippet
|
||||
showing how SCHED_DEADLINE reservations can be created by a real-time
|
||||
application developer.
|
||||
application developer::
|
||||
|
||||
#define _GNU_SOURCE
|
||||
#include <unistd.h>
|
||||
@ -4,6 +4,7 @@
|
||||
|
||||
|
||||
1. OVERVIEW
|
||||
============
|
||||
|
||||
CFS stands for "Completely Fair Scheduler," and is the new "desktop" process
|
||||
scheduler implemented by Ingo Molnar and merged in Linux 2.6.23. It is the
|
||||
@ -27,6 +28,7 @@ is its actual runtime normalized to the total number of running tasks.
|
||||
|
||||
|
||||
2. FEW IMPLEMENTATION DETAILS
|
||||
==============================
|
||||
|
||||
In CFS the virtual runtime is expressed and tracked via the per-task
|
||||
p->se.vruntime (nanosec-unit) value. This way, it's possible to accurately
|
||||
@ -49,6 +51,7 @@ algorithm variants to recognize sleepers.
|
||||
|
||||
|
||||
3. THE RBTREE
|
||||
==============
|
||||
|
||||
CFS's design is quite radical: it does not use the old data structures for the
|
||||
runqueues, but it uses a time-ordered rbtree to build a "timeline" of future
|
||||
@ -84,6 +87,7 @@ picked and the current task is preempted.
|
||||
|
||||
|
||||
4. SOME FEATURES OF CFS
|
||||
========================
|
||||
|
||||
CFS uses nanosecond granularity accounting and does not rely on any jiffies or
|
||||
other HZ detail. Thus the CFS scheduler has no notion of "timeslices" in the
|
||||
@ -113,6 +117,7 @@ result.
|
||||
|
||||
|
||||
5. Scheduling policies
|
||||
======================
|
||||
|
||||
CFS implements three scheduling policies:
|
||||
|
||||
@ -137,6 +142,7 @@ SCHED_IDLE.
|
||||
|
||||
|
||||
6. SCHEDULING CLASSES
|
||||
======================
|
||||
|
||||
The new CFS scheduler has been designed in such a way to introduce "Scheduling
|
||||
Classes," an extensible hierarchy of scheduler modules. These modules
|
||||
@ -197,6 +203,7 @@ This is the (partial) list of the hooks:
|
||||
|
||||
|
||||
7. GROUP SCHEDULER EXTENSIONS TO CFS
|
||||
=====================================
|
||||
|
||||
Normally, the scheduler operates on individual tasks and strives to provide
|
||||
fair CPU time to each task. Sometimes, it may be desirable to group tasks and
|
||||
@ -219,7 +226,7 @@ SCHED_BATCH) tasks.
|
||||
|
||||
When CONFIG_FAIR_GROUP_SCHED is defined, a "cpu.shares" file is created for each
|
||||
group created using the pseudo filesystem. See example steps below to create
|
||||
task groups and modify their CPU share using the "cgroups" pseudo filesystem.
|
||||
task groups and modify their CPU share using the "cgroups" pseudo filesystem::
|
||||
|
||||
# mount -t tmpfs cgroup_root /sys/fs/cgroup
|
||||
# mkdir /sys/fs/cgroup/cpu
|
||||
@ -1,3 +1,7 @@
|
||||
=================
|
||||
Scheduler Domains
|
||||
=================
|
||||
|
||||
Each CPU has a "base" scheduling domain (struct sched_domain). The domain
|
||||
hierarchy is built from these base domains via the ->parent pointer. ->parent
|
||||
MUST be NULL terminated, and domain structures should be per-CPU as they are
|
||||
@ -46,7 +50,9 @@ CPU's runqueue and the newly found busiest one and starts moving tasks from it
|
||||
to our runqueue. The exact number of tasks amounts to an imbalance previously
|
||||
computed while iterating over this sched domain's groups.
|
||||
|
||||
*** Implementing sched domains ***
|
||||
Implementing sched domains
|
||||
==========================
|
||||
|
||||
The "base" domain will "span" the first level of the hierarchy. In the case
|
||||
of SMT, you'll span all siblings of the physical CPU, with each group being
|
||||
a single virtual CPU.
|
||||
@ -12,7 +12,7 @@ with a minimal impact on throughput. This document aims at providing an
|
||||
introduction on how EAS works, what are the main design decisions behind it, and
|
||||
details what is needed to get it to run.
|
||||
|
||||
Before going any further, please note that at the time of writing:
|
||||
Before going any further, please note that at the time of writing::
|
||||
|
||||
/!\ EAS does not support platforms with symmetric CPU topologies /!\
|
||||
|
||||
@ -33,13 +33,13 @@ To make it clear from the start:
|
||||
- power = energy/time = [joule/second] = [watt]
|
||||
|
||||
The goal of EAS is to minimize energy, while still getting the job done. That
|
||||
is, we want to maximize:
|
||||
is, we want to maximize::
|
||||
|
||||
performance [inst/s]
|
||||
--------------------
|
||||
power [W]
|
||||
|
||||
which is equivalent to minimizing:
|
||||
which is equivalent to minimizing::
|
||||
|
||||
energy [J]
|
||||
-----------
|
||||
@ -97,7 +97,7 @@ domains can contain duplicate elements.
|
||||
|
||||
Example 1.
|
||||
Let us consider a platform with 12 CPUs, split in 3 performance domains
|
||||
(pd0, pd4 and pd8), organized as follows:
|
||||
(pd0, pd4 and pd8), organized as follows::
|
||||
|
||||
CPUs: 0 1 2 3 4 5 6 7 8 9 10 11
|
||||
PDs: |--pd0--|--pd4--|---pd8---|
|
||||
@ -108,6 +108,7 @@ Example 1.
|
||||
containing 6 CPUs. The two root domains are denoted rd1 and rd2 in the
|
||||
above figure. Since pd4 intersects with both rd1 and rd2, it will be
|
||||
present in the linked list '->pd' attached to each of them:
|
||||
|
||||
* rd1->pd: pd0 -> pd4
|
||||
* rd2->pd: pd4 -> pd8
|
||||
|
||||
@ -159,7 +160,7 @@ Example 2.
|
||||
Each performance domain has three Operating Performance Points (OPPs).
|
||||
The CPU capacity and power cost associated with each OPP is listed in
|
||||
the Energy Model table. The util_avg of P is shown on the figures
|
||||
below as 'PP'.
|
||||
below as 'PP'::
|
||||
|
||||
CPU util.
|
||||
1024 - - - - - - - Energy Model
|
||||
@ -188,8 +189,7 @@ Example 2.
|
||||
(which is coherent with the behaviour of the schedutil CPUFreq
|
||||
governor, see Section 6. for more details on this topic).
|
||||
|
||||
Case 1. P is migrated to CPU1
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
**Case 1. P is migrated to CPU1**::
|
||||
|
||||
1024 - - - - - - -
|
||||
|
||||
@ -207,8 +207,7 @@ Example 2.
|
||||
CPU0 CPU1 CPU2 CPU3
|
||||
|
||||
|
||||
Case 2. P is migrated to CPU3
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
**Case 2. P is migrated to CPU3**::
|
||||
|
||||
1024 - - - - - - -
|
||||
|
||||
@ -226,8 +225,7 @@ Example 2.
|
||||
CPU0 CPU1 CPU2 CPU3
|
||||
|
||||
|
||||
Case 3. P stays on prev_cpu / CPU 0
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
**Case 3. P stays on prev_cpu / CPU 0**::
|
||||
|
||||
1024 - - - - - - -
|
||||
|
||||
@ -325,6 +323,8 @@ section lists these dependencies and provides hints as to how they can be met.
|
||||
|
||||
|
||||
6.1 - Asymmetric CPU topology
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
|
||||
As mentioned in the introduction, EAS is only supported on platforms with
|
||||
asymmetric CPU topologies for now. This requirement is checked at run-time by
|
||||
@ -348,6 +348,7 @@ could be amended in the future if proven otherwise.
|
||||
|
||||
|
||||
6.2 - Energy Model presence
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
EAS uses the EM of a platform to estimate the impact of scheduling decisions on
|
||||
energy. So, your platform must provide power cost tables to the EM framework in
|
||||
@ -359,6 +360,7 @@ EM has been registered in order to start EAS.
|
||||
|
||||
|
||||
6.3 - Energy Model complexity
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
The task wake-up path is very latency-sensitive. When the EM of a platform is
|
||||
too complex (too many CPUs, too many performance domains, too many performance
|
||||
@ -389,6 +391,7 @@ two possible options:
|
||||
|
||||
|
||||
6.4 - Schedutil governor
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
EAS tries to predict at which OPP will the CPUs be running in the close future
|
||||
in order to estimate their energy consumption. To do so, it is assumed that OPPs
|
||||
@ -406,6 +409,7 @@ Using EAS with any other governor than schedutil is not supported.
|
||||
|
||||
|
||||
6.5 Scale-invariant utilization signals
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
In order to make accurate prediction across CPUs and for all performance
|
||||
states, EAS needs frequency-invariant and CPU-invariant PELT signals. These can
|
||||
@ -417,6 +421,7 @@ supported.
|
||||
|
||||
|
||||
6.6 Multithreading (SMT)
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
EAS in its current form is SMT unaware and is not able to leverage
|
||||
multithreaded hardware to save energy. EAS considers threads as independent
|
||||
@ -1,3 +1,7 @@
|
||||
=====================
|
||||
Scheduler Nice Design
|
||||
=====================
|
||||
|
||||
This document explains the thinking about the revamped and streamlined
|
||||
nice-levels implementation in the new Linux scheduler.
|
||||
|
||||
@ -14,7 +18,7 @@ much stronger than they were before in 2.4 (and people were happy about
|
||||
that change), and we also intentionally calibrated the linear timeslice
|
||||
rule so that nice +19 level would be _exactly_ 1 jiffy. To better
|
||||
understand it, the timeslice graph went like this (cheesy ASCII art
|
||||
alert!):
|
||||
alert!)::
|
||||
|
||||
|
||||
A
|
||||
@ -1,8 +1,8 @@
|
||||
==========================
|
||||
Real-Time group scheduling
|
||||
--------------------------
|
||||
==========================
|
||||
|
||||
CONTENTS
|
||||
========
|
||||
.. CONTENTS
|
||||
|
||||
0. WARNING
|
||||
1. Overview
|
||||
@ -159,9 +159,11 @@ Consider two sibling groups A and B; both have 50% bandwidth, but A's
|
||||
period is twice the length of B's.
|
||||
|
||||
* group A: period=100000us, runtime=50000us
|
||||
|
||||
- this runs for 0.05s once every 0.1s
|
||||
|
||||
* group B: period= 50000us, runtime=25000us
|
||||
|
||||
- this runs for 0.025s twice every 0.1s (or once every 0.05 sec).
|
||||
|
||||
This means that currently a while (1) loop in A will run for the full period of
|
||||
@ -1,3 +1,7 @@
|
||||
====================
|
||||
Scheduler Statistics
|
||||
====================
|
||||
|
||||
Version 15 of schedstats dropped counters for some sched_yield:
|
||||
yld_exp_empty, yld_act_empty and yld_both_empty. Otherwise, it is
|
||||
identical to version 14.
|
||||
@ -35,19 +39,23 @@ CPU statistics
|
||||
cpu<N> 1 2 3 4 5 6 7 8 9
|
||||
|
||||
First field is a sched_yield() statistic:
|
||||
|
||||
1) # of times sched_yield() was called
|
||||
|
||||
Next three are schedule() statistics:
|
||||
|
||||
2) This field is a legacy array expiration count field used in the O(1)
|
||||
scheduler. We kept it for ABI compatibility, but it is always set to zero.
|
||||
3) # of times schedule() was called
|
||||
4) # of times schedule() left the processor idle
|
||||
|
||||
Next two are try_to_wake_up() statistics:
|
||||
|
||||
5) # of times try_to_wake_up() was called
|
||||
6) # of times try_to_wake_up() was called to wake up the local cpu
|
||||
|
||||
Next three are statistics describing scheduling latency:
|
||||
|
||||
7) sum of all time spent running by tasks on this processor (in jiffies)
|
||||
8) sum of all time spent waiting to run by tasks on this processor (in
|
||||
jiffies)
|
||||
@ -83,7 +91,6 @@ of idleness (idle, busy, and newly idle):
|
||||
not find a busier queue while the cpu was idle
|
||||
8) # of times in this domain a busier queue was found while the
|
||||
cpu was idle but no busier group was found
|
||||
|
||||
9) # of times in this domain load_balance() was called when the
|
||||
cpu was busy
|
||||
10) # of times in this domain load_balance() checked but found the
|
||||
@ -117,21 +124,25 @@ of idleness (idle, busy, and newly idle):
|
||||
was just becoming idle but no busier group was found
|
||||
|
||||
Next three are active_load_balance() statistics:
|
||||
|
||||
25) # of times active_load_balance() was called
|
||||
26) # of times active_load_balance() tried to move a task and failed
|
||||
27) # of times active_load_balance() successfully moved a task
|
||||
|
||||
Next three are sched_balance_exec() statistics:
|
||||
|
||||
28) sbe_cnt is not used
|
||||
29) sbe_balanced is not used
|
||||
30) sbe_pushed is not used
|
||||
|
||||
Next three are sched_balance_fork() statistics:
|
||||
|
||||
31) sbf_cnt is not used
|
||||
32) sbf_balanced is not used
|
||||
33) sbf_pushed is not used
|
||||
|
||||
Next three are try_to_wake_up() statistics:
|
||||
|
||||
34) # of times in this domain try_to_wake_up() awoke a task that
|
||||
last ran on a different cpu in this domain
|
||||
35) # of times in this domain try_to_wake_up() moved a task to the
|
||||
@ -139,10 +150,11 @@ of idleness (idle, busy, and newly idle):
|
||||
36) # of times in this domain try_to_wake_up() started passive balancing
|
||||
|
||||
/proc/<pid>/schedstat
|
||||
----------------
|
||||
---------------------
|
||||
schedstats also adds a new /proc/<pid>/schedstat file to include some of
|
||||
the same information on a per-process level. There are three fields in
|
||||
this file correlating for that process to:
|
||||
|
||||
1) time spent on the cpu
|
||||
2) time spent waiting on a runqueue
|
||||
3) # of timeslices run on this cpu
|
||||
@ -151,4 +163,5 @@ A program could be easily written to make use of these extra fields to
|
||||
report on how well a particular process or set of processes is faring
|
||||
under the scheduler's policies. A simple version of such a program is
|
||||
available at
|
||||
|
||||
http://eaglet.rain.com/rick/linux/schedstat/v12/latency.c
|
||||
5
Documentation/scheduler/text_files.rst
Normal file
5
Documentation/scheduler/text_files.rst
Normal file
@ -0,0 +1,5 @@
|
||||
Scheduler pelt c program
|
||||
------------------------
|
||||
|
||||
.. literalinclude:: sched-pelt.c
|
||||
:language: c
|
||||
@ -99,7 +99,7 @@ Local allocation will tend to keep subsequent access to the allocated memory
|
||||
as long as the task on whose behalf the kernel allocated some memory does not
|
||||
later migrate away from that memory. The Linux scheduler is aware of the
|
||||
NUMA topology of the platform--embodied in the "scheduling domains" data
|
||||
structures [see Documentation/scheduler/sched-domains.txt]--and the scheduler
|
||||
structures [see Documentation/scheduler/sched-domains.rst]--and the scheduler
|
||||
attempts to minimize task migration to distant scheduling domains. However,
|
||||
the scheduler does not take a task's NUMA footprint into account directly.
|
||||
Thus, under sufficient imbalance, tasks can migrate between nodes, remote
|
||||
|
||||
@ -734,7 +734,7 @@ menuconfig CGROUPS
|
||||
use with process control subsystems such as Cpusets, CFS, memory
|
||||
controls or device isolation.
|
||||
See
|
||||
- Documentation/scheduler/sched-design-CFS.txt (CFS)
|
||||
- Documentation/scheduler/sched-design-CFS.rst (CFS)
|
||||
- Documentation/cgroup-v1/ (features for grouping, isolation
|
||||
and resource control)
|
||||
|
||||
@ -835,7 +835,7 @@ config CFS_BANDWIDTH
|
||||
tasks running within the fair group scheduler. Groups with no limit
|
||||
set are considered to be unconstrained and will run with no
|
||||
restriction.
|
||||
See Documentation/scheduler/sched-bwc.txt for more information.
|
||||
See Documentation/scheduler/sched-bwc.rst for more information.
|
||||
|
||||
config RT_GROUP_SCHED
|
||||
bool "Group scheduling for SCHED_RR/FIFO"
|
||||
@ -846,7 +846,7 @@ config RT_GROUP_SCHED
|
||||
to task groups. If enabled, it will also make it impossible to
|
||||
schedule realtime tasks for non-root users until you allocate
|
||||
realtime bandwidth for them.
|
||||
See Documentation/scheduler/sched-rt-group.txt for more information.
|
||||
See Documentation/scheduler/sched-rt-group.rst for more information.
|
||||
|
||||
endif #CGROUP_SCHED
|
||||
|
||||
|
||||
@ -726,7 +726,7 @@ static void replenish_dl_entity(struct sched_dl_entity *dl_se,
|
||||
* refill the runtime and set the deadline a period in the future,
|
||||
* because keeping the current (absolute) deadline of the task would
|
||||
* result in breaking guarantees promised to other tasks (refer to
|
||||
* Documentation/scheduler/sched-deadline.txt for more information).
|
||||
* Documentation/scheduler/sched-deadline.rst for more information).
|
||||
*
|
||||
* This function returns true if:
|
||||
*
|
||||
|
||||
Loading…
Reference in New Issue
Block a user