diff options
Diffstat (limited to 'Documentation/RCU')
| -rw-r--r-- | Documentation/RCU/RTFP.txt | 210 | ||||
| -rw-r--r-- | Documentation/RCU/rcu.txt | 19 | ||||
| -rw-r--r-- | Documentation/RCU/torture.txt | 11 |
3 files changed, 221 insertions, 19 deletions
diff --git a/Documentation/RCU/RTFP.txt b/Documentation/RCU/RTFP.txt index 6221464d1a7e..39ad8f56783a 100644 --- a/Documentation/RCU/RTFP.txt +++ b/Documentation/RCU/RTFP.txt @@ -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). +" +} + diff --git a/Documentation/RCU/rcu.txt b/Documentation/RCU/rcu.txt index f84407cba816..95821a29ae41 100644 --- a/Documentation/RCU/rcu.txt +++ b/Documentation/RCU/rcu.txt @@ -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? diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt index 25a3c3f7d378..2967a65269d8 100644 --- a/Documentation/RCU/torture.txt +++ b/Documentation/RCU/torture.txt @@ -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 |