mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-11-20 08:38:24 +08:00
Preempt-RCU: update RCU Documentation.
This patch updates the RCU documentation to reflect preemptible RCU as well as recent publications. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Gautham R Shenoy <ego@in.ibm.com> Reviewed-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Paul E. McKenney
Ingo Molnar
parent
eaf649e9fe
commit
f85d6c7168
@ -9,8 +9,8 @@ The first thing resembling RCU was published in 1980, when Kung and Lehman
|
||||
[Kung80] recommended use of a garbage collector to defer destruction
|
||||
of nodes in a parallel binary search tree in order to simplify its
|
||||
implementation. This works well in environments that have garbage
|
||||
collectors, but current production garbage collectors incur significant
|
||||
read-side overhead.
|
||||
collectors, but most production garbage collectors incur significant
|
||||
overhead.
|
||||
|
||||
In 1982, Manber and Ladner [Manber82,Manber84] recommended deferring
|
||||
destruction until all threads running at that time have terminated, again
|
||||
@ -99,16 +99,25 @@ locking, reduces contention, reduces memory latency for readers, and
|
||||
parallelizes pipeline stalls and memory latency for writers. However,
|
||||
these techniques still impose significant read-side overhead in the
|
||||
form of memory barriers. Researchers at Sun worked along similar lines
|
||||
in the same timeframe [HerlihyLM02,HerlihyLMS03]. These techniques
|
||||
can be thought of as inside-out reference counts, where the count is
|
||||
represented by the number of hazard pointers referencing a given data
|
||||
structure (rather than the more conventional counter field within the
|
||||
data structure itself).
|
||||
in the same timeframe [HerlihyLM02]. These techniques can be thought
|
||||
of as inside-out reference counts, where the count is represented by the
|
||||
number of hazard pointers referencing a given data structure (rather than
|
||||
the more conventional counter field within the data structure itself).
|
||||
|
||||
By the same token, RCU can be thought of as a "bulk reference count",
|
||||
where some form of reference counter covers all reference by a given CPU
|
||||
or thread during a set timeframe. This timeframe is related to, but
|
||||
not necessarily exactly the same as, an RCU grace period. In classic
|
||||
RCU, the reference counter is the per-CPU bit in the "bitmask" field,
|
||||
and each such bit covers all references that might have been made by
|
||||
the corresponding CPU during the prior grace period. Of course, RCU
|
||||
can be thought of in other terms as well.
|
||||
|
||||
In 2003, the K42 group described how RCU could be used to create
|
||||
hot-pluggable implementations of operating-system functions. Later that
|
||||
year saw a paper describing an RCU implementation of System V IPC
|
||||
[Arcangeli03], and an introduction to RCU in Linux Journal [McKenney03a].
|
||||
hot-pluggable implementations of operating-system functions [Appavoo03a].
|
||||
Later that year saw a paper describing an RCU implementation of System
|
||||
V IPC [Arcangeli03], and an introduction to RCU in Linux Journal
|
||||
[McKenney03a].
|
||||
|
||||
2004 has seen a Linux-Journal article on use of RCU in dcache
|
||||
[McKenney04a], a performance comparison of locking to RCU on several
|
||||
@ -117,10 +126,19 @@ number of operating-system kernels [PaulEdwardMcKenneyPhD], a paper
|
||||
describing how to make RCU safe for soft-realtime applications [Sarma04c],
|
||||
and a paper describing SELinux performance with RCU [JamesMorris04b].
|
||||
|
||||
2005 has seen further adaptation of RCU to realtime use, permitting
|
||||
2005 brought further adaptation of RCU to realtime use, permitting
|
||||
preemption of RCU realtime critical sections [PaulMcKenney05a,
|
||||
PaulMcKenney05b].
|
||||
|
||||
2006 saw the first best-paper award for an RCU paper [ThomasEHart2006a],
|
||||
as well as further work on efficient implementations of preemptible
|
||||
RCU [PaulEMcKenney2006b], but priority-boosting of RCU read-side critical
|
||||
sections proved elusive. An RCU implementation permitting general
|
||||
blocking in read-side critical sections appeared [PaulEMcKenney2006c],
|
||||
Robert Olsson described an RCU-protected trie-hash combination
|
||||
[RobertOlsson2006a].
|
||||
|
||||
|
||||
Bibtex Entries
|
||||
|
||||
@article{Kung80
|
||||
@ -203,6 +221,41 @@ Bibtex Entries
|
||||
,Address="New Orleans, LA"
|
||||
}
|
||||
|
||||
@conference{Pu95a,
|
||||
Author = "Calton Pu and Tito Autrey and Andrew Black and Charles Consel and
|
||||
Crispin Cowan and Jon Inouye and Lakshmi Kethana and Jonathan Walpole and
|
||||
Ke Zhang",
|
||||
Title = "Optimistic Incremental Specialization: Streamlining a Commercial
|
||||
Operating System",
|
||||
Booktitle = "15\textsuperscript{th} ACM Symposium on
|
||||
Operating Systems Principles (SOSP'95)",
|
||||
address = "Copper Mountain, CO",
|
||||
month="December",
|
||||
year="1995",
|
||||
pages="314-321",
|
||||
annotation="
|
||||
Uses a replugger, but with a flag to signal when people are
|
||||
using the resource at hand. Only one reader at a time.
|
||||
"
|
||||
}
|
||||
|
||||
@conference{Cowan96a,
|
||||
Author = "Crispin Cowan and Tito Autrey and Charles Krasic and
|
||||
Calton Pu and Jonathan Walpole",
|
||||
Title = "Fast Concurrent Dynamic Linking for an Adaptive Operating System",
|
||||
Booktitle = "International Conference on Configurable Distributed Systems
|
||||
(ICCDS'96)",
|
||||
address = "Annapolis, MD",
|
||||
month="May",
|
||||
year="1996",
|
||||
pages="108",
|
||||
isbn="0-8186-7395-8",
|
||||
annotation="
|
||||
Uses a replugger, but with a counter to signal when people are
|
||||
using the resource at hand. Allows multiple readers.
|
||||
"
|
||||
}
|
||||
|
||||
@techreport{Slingwine95
|
||||
,author="John D. Slingwine and Paul E. McKenney"
|
||||
,title="Apparatus and Method for Achieving Reduced Overhead Mutual
|
||||
@ -312,6 +365,49 @@ Andrea Arcangeli and Andi Kleen and Orran Krieger and Rusty Russell"
|
||||
[Viewed June 23, 2004]"
|
||||
}
|
||||
|
||||
@conference{Michael02a
|
||||
,author="Maged M. Michael"
|
||||
,title="Safe Memory Reclamation for Dynamic Lock-Free Objects Using Atomic
|
||||
Reads and Writes"
|
||||
,Year="2002"
|
||||
,Month="August"
|
||||
,booktitle="{Proceedings of the 21\textsuperscript{st} Annual ACM
|
||||
Symposium on Principles of Distributed Computing}"
|
||||
,pages="21-30"
|
||||
,annotation="
|
||||
Each thread keeps an array of pointers to items that it is
|
||||
currently referencing. Sort of an inside-out garbage collection
|
||||
mechanism, but one that requires the accessing code to explicitly
|
||||
state its needs. Also requires read-side memory barriers on
|
||||
most architectures.
|
||||
"
|
||||
}
|
||||
|
||||
@conference{Michael02b
|
||||
,author="Maged M. Michael"
|
||||
,title="High Performance Dynamic Lock-Free Hash Tables and List-Based Sets"
|
||||
,Year="2002"
|
||||
,Month="August"
|
||||
,booktitle="{Proceedings of the 14\textsuperscript{th} Annual ACM
|
||||
Symposium on Parallel
|
||||
Algorithms and Architecture}"
|
||||
,pages="73-82"
|
||||
,annotation="
|
||||
Like the title says...
|
||||
"
|
||||
}
|
||||
|
||||
@InProceedings{HerlihyLM02
|
||||
,author={Maurice Herlihy and Victor Luchangco and Mark Moir}
|
||||
,title="The Repeat Offender Problem: A Mechanism for Supporting Dynamic-Sized,
|
||||
Lock-Free Data Structures"
|
||||
,booktitle={Proceedings of 16\textsuperscript{th} International
|
||||
Symposium on Distributed Computing}
|
||||
,year=2002
|
||||
,month="October"
|
||||
,pages="339-353"
|
||||
}
|
||||
|
||||
@article{Appavoo03a
|
||||
,author="J. Appavoo and K. Hui and C. A. N. Soules and R. W. Wisniewski and
|
||||
D. M. {Da Silva} and O. Krieger and M. A. Auslander and D. J. Edelsohn and
|
||||
@ -447,3 +543,95 @@ Oregon Health and Sciences University"
|
||||
Realtime turns into making RCU yet more realtime friendly.
|
||||
"
|
||||
}
|
||||
|
||||
@conference{ThomasEHart2006a
|
||||
,Author="Thomas E. Hart and Paul E. McKenney and Angela Demke Brown"
|
||||
,Title="Making Lockless Synchronization Fast: Performance Implications
|
||||
of Memory Reclamation"
|
||||
,Booktitle="20\textsuperscript{th} {IEEE} International Parallel and
|
||||
Distributed Processing Symposium"
|
||||
,month="April"
|
||||
,year="2006"
|
||||
,day="25-29"
|
||||
,address="Rhodes, Greece"
|
||||
,annotation="
|
||||
Compares QSBR (AKA "classic RCU"), HPBR, EBR, and lock-free
|
||||
reference counting.
|
||||
"
|
||||
}
|
||||
|
||||
@Conference{PaulEMcKenney2006b
|
||||
,Author="Paul E. McKenney and Dipankar Sarma and Ingo Molnar and
|
||||
Suparna Bhattacharya"
|
||||
,Title="Extending RCU for Realtime and Embedded Workloads"
|
||||
,Booktitle="{Ottawa Linux Symposium}"
|
||||
,Month="July"
|
||||
,Year="2006"
|
||||
,pages="v2 123-138"
|
||||
,note="Available:
|
||||
\url{http://www.linuxsymposium.org/2006/view_abstract.php?content_key=184}
|
||||
\url{http://www.rdrop.com/users/paulmck/RCU/OLSrtRCU.2006.08.11a.pdf}
|
||||
[Viewed January 1, 2007]"
|
||||
,annotation="
|
||||
Described how to improve the -rt implementation of realtime RCU.
|
||||
"
|
||||
}
|
||||
|
||||
@unpublished{PaulEMcKenney2006c
|
||||
,Author="Paul E. McKenney"
|
||||
,Title="Sleepable {RCU}"
|
||||
,month="October"
|
||||
,day="9"
|
||||
,year="2006"
|
||||
,note="Available:
|
||||
\url{http://lwn.net/Articles/202847/}
|
||||
Revised:
|
||||
\url{http://www.rdrop.com/users/paulmck/RCU/srcu.2007.01.14a.pdf}
|
||||
[Viewed August 21, 2006]"
|
||||
,annotation="
|
||||
LWN article introducing SRCU.
|
||||
"
|
||||
}
|
||||
|
||||
@unpublished{RobertOlsson2006a
|
||||
,Author="Robert Olsson and Stefan Nilsson"
|
||||
,Title="{TRASH}: A dynamic {LC}-trie and hash data structure"
|
||||
,month="August"
|
||||
,day="18"
|
||||
,year="2006"
|
||||
,note="Available:
|
||||
\url{http://www.nada.kth.se/~snilsson/public/papers/trash/trash.pdf}
|
||||
[Viewed February 24, 2007]"
|
||||
,annotation="
|
||||
RCU-protected dynamic trie-hash combination.
|
||||
"
|
||||
}
|
||||
|
||||
@unpublished{ThomasEHart2007a
|
||||
,Author="Thomas E. Hart and Paul E. McKenney and Angela Demke Brown and Jonathan Walpole"
|
||||
,Title="Performance of memory reclamation for lockless synchronization"
|
||||
,journal="J. Parallel Distrib. Comput."
|
||||
,year="2007"
|
||||
,note="To appear in J. Parallel Distrib. Comput.
|
||||
\url{doi=10.1016/j.jpdc.2007.04.010}"
|
||||
,annotation={
|
||||
Compares QSBR (AKA "classic RCU"), HPBR, EBR, and lock-free
|
||||
reference counting. Journal version of ThomasEHart2006a.
|
||||
}
|
||||
}
|
||||
|
||||
@unpublished{PaulEMcKenney2007QRCUspin
|
||||
,Author="Paul E. McKenney"
|
||||
,Title="Using Promela and Spin to verify parallel algorithms"
|
||||
,month="August"
|
||||
,day="1"
|
||||
,year="2007"
|
||||
,note="Available:
|
||||
\url{http://lwn.net/Articles/243851/}
|
||||
[Viewed September 8, 2007]"
|
||||
,annotation="
|
||||
LWN article describing Promela and spin, and also using Oleg
|
||||
Nesterov's QRCU as an example (with Paul McKenney's fastpath).
|
||||
"
|
||||
}
|
||||
|
||||
|
||||
@ -36,6 +36,14 @@ o How can the updater tell when a grace period has completed
|
||||
executed in user mode, or executed in the idle loop, we can
|
||||
safely free up that item.
|
||||
|
||||
Preemptible variants of RCU (CONFIG_PREEMPT_RCU) get the
|
||||
same effect, but require that the readers manipulate CPU-local
|
||||
counters. These counters allow limited types of blocking
|
||||
within RCU read-side critical sections. SRCU also uses
|
||||
CPU-local counters, and permits general blocking within
|
||||
RCU read-side critical sections. These two variants of
|
||||
RCU detect grace periods by sampling these counters.
|
||||
|
||||
o If I am running on a uniprocessor kernel, which can only do one
|
||||
thing at a time, why should I wait for a grace period?
|
||||
|
||||
@ -46,7 +54,10 @@ o How can I see where RCU is currently used in the Linux kernel?
|
||||
Search for "rcu_read_lock", "rcu_read_unlock", "call_rcu",
|
||||
"rcu_read_lock_bh", "rcu_read_unlock_bh", "call_rcu_bh",
|
||||
"srcu_read_lock", "srcu_read_unlock", "synchronize_rcu",
|
||||
"synchronize_net", and "synchronize_srcu".
|
||||
"synchronize_net", "synchronize_srcu", and the other RCU
|
||||
primitives. Or grab one of the cscope databases from:
|
||||
|
||||
http://www.rdrop.com/users/paulmck/RCU/linuxusage/rculocktab.html
|
||||
|
||||
o What guidelines should I follow when writing code that uses RCU?
|
||||
|
||||
@ -67,7 +78,11 @@ o I hear that RCU is patented? What is with that?
|
||||
|
||||
o I hear that RCU needs work in order to support realtime kernels?
|
||||
|
||||
Yes, work in progress.
|
||||
This work is largely completed. Realtime-friendly RCU can be
|
||||
enabled via the CONFIG_PREEMPT_RCU kernel configuration parameter.
|
||||
However, work is in progress for enabling priority boosting of
|
||||
preempted RCU read-side critical sections.This is needed if you
|
||||
have CPU-bound realtime threads.
|
||||
|
||||
o Where can I find more information on RCU?
|
||||
|
||||
|
||||
@ -46,12 +46,13 @@ stat_interval The number of seconds between output of torture
|
||||
|
||||
shuffle_interval
|
||||
The number of seconds to keep the test threads affinitied
|
||||
to a particular subset of the CPUs. Used in conjunction
|
||||
with test_no_idle_hz.
|
||||
to a particular subset of the CPUs, defaults to 5 seconds.
|
||||
Used in conjunction with test_no_idle_hz.
|
||||
|
||||
test_no_idle_hz Whether or not to test the ability of RCU to operate in
|
||||
a kernel that disables the scheduling-clock interrupt to
|
||||
idle CPUs. Boolean parameter, "1" to test, "0" otherwise.
|
||||
Defaults to omitting this test.
|
||||
|
||||
torture_type The type of RCU to test: "rcu" for the rcu_read_lock() API,
|
||||
"rcu_sync" for rcu_read_lock() with synchronous reclamation,
|
||||
@ -82,8 +83,6 @@ be evident. ;-)
|
||||
|
||||
The entries are as follows:
|
||||
|
||||
o "ggp": The number of counter flips (or batches) since boot.
|
||||
|
||||
o "rtc": The hexadecimal address of the structure currently visible
|
||||
to readers.
|
||||
|
||||
@ -117,8 +116,8 @@ o "Reader Pipe": Histogram of "ages" of structures seen by readers.
|
||||
o "Reader Batch": Another histogram of "ages" of structures seen
|
||||
by readers, but in terms of counter flips (or batches) rather
|
||||
than in terms of grace periods. The legal number of non-zero
|
||||
entries is again two. The reason for this separate view is
|
||||
that it is easier to get the third entry to show up in the
|
||||
entries is again two. The reason for this separate view is that
|
||||
it is sometimes easier to get the third entry to show up in the
|
||||
"Reader Batch" list than in the "Reader Pipe" list.
|
||||
|
||||
o "Free-Block Circulation": Shows the number of torture structures
|
||||
|
||||
Loading…
Reference in New Issue
Block a user