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Documentation: scheduler: fix information on arch SD flags, sched_domain and sched_debug

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This document seems to be out of date for many, many years. Even it has
misspelled from the first day.
ARCH_HASH_SCHED_TUNE should be ARCH_HAS_SCHED_TUNE
ARCH_HASH_SCHED_DOMAIN should be ARCH_HAS_SCHED_DOMAIN

Since v2.6.14, kernel completely deleted the relevant code and even
arch_init_sched_domains() was deleted.

Right now, kernel is asking architectures to call set_sched_topology() to
override the default sched domains.

On the other hand, to print the schedule debug information, users need to
set sched_debug cmdline or enable it by sysfs entry. So this patch also
adds the description for sched_debug.

Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20201113115018.1628-1-song.bao.hua@hisilicon.com
This commit is contained in:
Barry Song 2020-11-14 00:50:18 +13:00 committed by Peter Zijlstra
parent b5b217346d
commit 9032dc2115
1 changed files with 11 additions and 15 deletions
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26
Documentation/scheduler/sched-domains.rst
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@ -65,21 +65,17 @@ of the SMP domain will span the entire machine, with each group having the
cpumask of a node. Or, you could do multi-level NUMA or Opteron, for example,
might have just one domain covering its one NUMA level.
The implementor should read comments in include/linux/sched.h:
struct sched_domain fields, SD_FLAG_*, SD_*_INIT to get an idea of
the specifics and what to tune.
The implementor should read comments in include/linux/sched/sd_flags.h:
SD_* to get an idea of the specifics and what to tune for the SD flags
of a sched_domain.
Architectures may retain the regular override the default SD_*_INIT flags
while using the generic domain builder in kernel/sched/core.c if they wish to
retain the traditional SMT->SMP->NUMA topology (or some subset of that). This
can be done by #define'ing ARCH_HASH_SCHED_TUNE.
Alternatively, the architecture may completely override the generic domain
builder by #define'ing ARCH_HASH_SCHED_DOMAIN, and exporting your
arch_init_sched_domains function. This function will attach domains to all
CPUs using cpu_attach_domain.
Architectures may override the generic domain builder and the default SD flags
for a given topology level by creating a sched_domain_topology_level array and
calling set_sched_topology() with this array as the parameter.
The sched-domains debugging infrastructure can be enabled by enabling
CONFIG_SCHED_DEBUG. This enables an error checking parse of the sched domains
which should catch most possible errors (described above). It also prints out
the domain structure in a visual format.
CONFIG_SCHED_DEBUG and adding 'sched_debug' to your cmdline. If you forgot to
tweak your cmdline, you can also flip the /sys/kernel/debug/sched_debug
knob. This enables an error checking parse of the sched domains which should
catch most possible errors (described above). It also prints out the domain
structure in a visual format.