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* Remove rcu_assign_pointer() penalty for NULL pointersPaul E. McKenney2008-02-06
| | | | | | | | | | | | | | | | | | | | | The rcu_assign_pointer() primitive currently unconditionally executes a memory barrier, even when a NULL pointer is being assigned. This has lead some to avoid using rcu_assign_pointer() for NULL pointers, which loses the self-documenting advantages of rcu_assign_pointer() This patch uses __builtin_const_p() to omit needless memory barriers for NULL-pointer assignments at compile time with no runtime penalty, as discussed in the following thread: http://www.mail-archive.com/netdev@vger.kernel.org/msg54852.html Tested on x86_64 and ppc64, also compiled the four cases (NULL/non-NULL and const/non-const) with gcc version 4.1.2, and hand-checked the assembly output. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* Preempt-RCU: implementationPaul E. McKenney2008-01-25
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch implements a new version of RCU which allows its read-side critical sections to be preempted. It uses a set of counter pairs to keep track of the read-side critical sections and flips them when all tasks exit read-side critical section. The details of this implementation can be found in this paper - http://www.rdrop.com/users/paulmck/RCU/OLSrtRCU.2006.08.11a.pdf and the article- http://lwn.net/Articles/253651/ This patch was developed as a part of the -rt kernel development and meant to provide better latencies when read-side critical sections of RCU don't disable preemption. As a consequence of keeping track of RCU readers, the readers have a slight overhead (optimizations in the paper). This implementation co-exists with the "classic" RCU implementations and can be switched to at compiler. Also includes RCU tracing summarized in debugfs. [ akpm@linux-foundation.org: build fixes on non-preempt architectures ] Signed-off-by: Gautham R Shenoy <ego@in.ibm.com> Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com> Reviewed-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* Preempt-RCU: reorganize RCU code into rcuclassic.c and rcupdate.cPaul E. McKenney2008-01-25
| | | | | | | | | | | | | This patch re-organizes the RCU code to enable multiple implementations of RCU. Users of RCU continues to include rcupdate.h and the RCU interfaces remain the same. This is in preparation for subsequently merging the preemptible RCU implementation. Signed-off-by: Gautham R Shenoy <ego@in.ibm.com> Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* Immunize rcu_dereference() against crazy compiler writersPaul E. McKenney2007-10-17
| | | | | | | | | | | | | Turns out that compiler writers are a bit more aggressive about optimizing than one might expect. This patch prevents a number of such optimizations from messing up rcu_deference(). This is not merely a theoretical problem, as evidenced by the rmb() in mce_log(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Acked-by: Josh Triplett <josh@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* lockdep: annotate rcu_read_{,un}lock{,_bh}Peter Zijlstra2007-10-11
| | | | | | | | | lockdep annotate rcu_read_{,un}lock{,_bh} in order to catch imbalanced usage. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* RCU: Remove prototype for nonexistent function synchronize_idle()Josh Triplett2007-08-11
| | | | | | | | | | | synchronize_idle() sounds like an interesting function, but we don't actually have it, so don't prototype it. Introduced in commit 9b06e818985d139fd9e82c28297f7744e1b484e1, in 2005. Signed-off-by: Josh Triplett <josh@kernel.org> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* [PATCH] RCU: CREDITS and MAINTAINERSJosh Triplett2006-10-04
| | | | | | | | | | | | | | Add MAINTAINERS entry for Read-Copy Update (RCU), listing Dipankar Sarma as maintainer, and giving the URL for Paul McKenney's RCU site. Add MAINTAINERS entry for rcutorture, listing myself as maintainer. Add CREDITS entries for developers of RCU, RCU variants, and rcutorture. Use Paul McKenney's preferred email address in include/linux/rcupdate.h . Signed-off-by: Josh Triplett <josh@freedesktop.org> Cc: Paul McKenney <paulmck@us.ibm.com> Cc: Dipankar Sarma <dipankar@in.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] rcu: simplify/improve batch tuningOleg Nesterov2006-10-04
| | | | | | | | | | | | | | | | | | | | Kill a hard-to-calculate 'rsinterval' boot parameter and per-cpu rcu_data.last_rs_qlen. Instead, it adds adds a flag rcu_ctrlblk.signaled, which records the fact that one of CPUs has sent a resched IPI since the last rcu_start_batch(). Roughly speaking, we need two rcu_start_batch()s in order to move callbacks from ->nxtlist to ->donelist. This means that when ->qlen exceeds qhimark and continues to grow, we should send a resched IPI, and then do it again after we gone through a quiescent state. On the other hand, if it was already sent, we don't need to do it again when another CPU detects overflow of the queue. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Acked-by: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] rcu: Add lock annotations to RCU locking primitivesJosh Triplett2006-06-30
| | | | | | | | | | | Add __acquire annotations to rcu_read_lock and rcu_read_lock_bh, and add __release annotations to rcu_read_unlock and rcu_read_unlock_bh. This allows sparse to detect improperly paired calls to these functions. Signed-off-by: Josh Triplett <josh@freedesktop.org> Acked-by: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] rcutorture: add call_rcu_bh() operationsPaul E. McKenney2006-06-27
| | | | | | | | | Add operations for the call_rcu_bh() variant of RCU. Also add an rcu_batches_completed_bh() function, which is needed by rcutorture. Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] Make RCU API inaccessible to non-GPL Linux kernel modulesPaul E. McKenney2006-06-23
| | | | | | | | | | | Remove synchronize_kernel() (deprecated 2-APR-2005 in http://lkml.org/lkml/2005/4/3/11) and makes the RCU API inaccessible to non-GPL Linux kernel modules (as was announced more than one year ago in http://lkml.org/lkml/2005/4/3/8). Tested on x86 and ppc64. Signed-off-by: "Paul E. McKenney" <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] RCU: introduce rcu_needs_cpu() interfaceHeiko Carstens2006-05-15
| | | | | | | | | | | | | | | With "Paul E. McKenney" <paulmck@us.ibm.com> Introduce rcu_needs_cpu() interface. This can be used to tell if there will be a new rcu batch on a cpu soon by looking at the curlist pointer. This can be used to avoid to enter a tickless idle state where the cpu would miss that a new batch is ready when rcu_start_batch would be called on a different cpu. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: "Paul E. McKenney" <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] kernel/rcupdate.c: make two structs staticAdrian Bunk2006-03-23
| | | | | | | | This patch makes two needlessly global structs static. Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] rcu batch tuningDipankar Sarma2006-03-08
| | | | | | | | | | | | | | | | | | | | | This patch adds new tunables for RCU queue and finished batches. There are two types of controls - number of completed RCU updates invoked in a batch (blimit) and monitoring for high rate of incoming RCUs on a cpu (qhimark, qlowmark). By default, the per-cpu batch limit is set to a small value. If the input RCU rate exceeds the high watermark, we do two things - force quiescent state on all cpus and set the batch limit of the CPU to INTMAX. Setting batch limit to INTMAX forces all finished RCUs to be processed in one shot. If we have more than INTMAX RCUs queued up, then we have bigger problems anyway. Once the incoming queued RCUs fall below the low watermark, the batch limit is set to the default. Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com> Cc: "Paul E. McKenney" <paulmck@us.ibm.com> Cc: "David S. Miller" <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] Fix comment to synchronize_sched()Paul E. McKenney2006-02-03
| | | | | | | | | | | | Fix to broken comment to synchronize_rcu() noted by Keith Owens. Also add sentence noting that synchronize_sched() and synchronize_rcu() are not necessarily identical. Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com> Cc: Keith Owens <kaos@sgi.com> Cc: Stephen Hemminger <shemminger@osdl.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] rcu: join rcu_ctrlblk and rcu_stateOleg Nesterov2006-01-10
| | | | | | | | | | | This patch moves rcu_state into the rcu_ctrlblk. I think there are no reasons why we should have 2 different variables to control rcu state. Every user of rcu_state has also "rcu_ctrlblk *rcp" in the parameter list. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Acked-by: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] rcu: uninline __rcu_pending()Oleg Nesterov2006-01-09
| | | | | | | | | | | | __rcu_pending() is rather fat and called twice from rcu_pending(). rcu_pending() has multiple callers, and not that small too. This patch uninlines both of them. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Acked-by: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] Change maxaligned_in_smp alignemnt macros to internodealigned_in_smp ↵Ravikiran G Thirumalai2006-01-08
| | | | | | | | | | | | | | | | | | | | | | | | macros ____cacheline_maxaligned_in_smp is currently used to align critical structures and avoid false sharing. It uses per-arch L1_CACHE_SHIFT_MAX and people find L1_CACHE_SHIFT_MAX useless. However, we have been using ____cacheline_maxaligned_in_smp to align structures on the internode cacheline size. As per Andi's suggestion, following patch kills ____cacheline_maxaligned_in_smp and introduces INTERNODE_CACHE_SHIFT, which defaults to L1_CACHE_SHIFT for all arches. Arches needing L3/Internode cacheline alignment can define INTERNODE_CACHE_SHIFT in the arch asm/cache.h. Patch replaces ____cacheline_maxaligned_in_smp with ____cacheline_internodealigned_in_smp With this patch, L1_CACHE_SHIFT_MAX can be killed Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org> Signed-off-by: Shai Fultheim <shai@scalex86.org> Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] add rcu_barrier() synchronization pointDipankar Sarma2005-12-12
| | | | | | | | | | | | | | | | | | | This introduces a new interface - rcu_barrier() which waits until all the RCUs queued until this call have been completed. Reiser4 needs this, because we do more than just freeing memory object in our RCU callback: we also remove it from the list hanging off super-block. This means, that before freeing reiser4-specific portion of super-block (during umount) we have to wait until all pending RCU callbacks are executed. The only change of reiser4 made to the original patch, is exporting of rcu_barrier(). Cc: Hans Reiser <reiser@namesys.com> Cc: Vladimir V. Saveliev <vs@namesys.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] RCU torture-testing kernel modulePaul E. McKenney2005-10-30
| | | | | | | | | | | | | | | | | | | | This patch is a rewrite of the one submitted on October 1st, using modules (http://marc.theaimsgroup.com/?l=linux-kernel&m=112819093522998&w=2). This rewrite adds a tristate CONFIG_RCU_TORTURE_TEST, which enables an intense torture test of the RCU infratructure. This is needed due to the continued changes to the RCU infrastructure to accommodate dynamic ticks, CPU hotplug, realtime, and so on. Most of the code is in a separate file that is compiled only if the CONFIG variable is set. Documentation on how to run the test and interpret the output is also included. This code has been tested on i386 and ppc64, and an earlier version of the code has received extensive testing on a number of architectures as part of the PREEMPT_RT patchset. Signed-off-by: "Paul E. McKenney" <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] rcu: keep rcu callback event counterEric Dumazet2005-10-17
| | | | | | | | | This makes call_rcu() keep track of how many events there are on the RCU list, and cause a reschedule event when the list gets too long. This helps keep RCU event lists down. Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] files: fix rcu initializersDipankar Sarma2005-09-09
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | First of a number of files_lock scaability patches. Here are the x86 numbers - tiobench on a 4(8)-way (HT) P4 system on ramdisk : (lockfree) Test 2.6.10-vanilla Stdev 2.6.10-fd Stdev ------------------------------------------------------------- Seqread 1400.8 11.52 1465.4 34.27 Randread 1594 8.86 2397.2 29.21 Seqwrite 242.72 3.47 238.46 6.53 Randwrite 445.74 9.15 446.4 9.75 The performance improvement is very significant. We are getting killed by the cacheline bouncing of the files_struct lock here. Writes on ramdisk (ext2) seems to vary just too much to get any meaningful number. Also, With Tridge's thread_perf test on a 4(8)-way (HT) P4 xeon system : 2.6.12-rc5-vanilla : Running test 'readwrite' with 8 tasks Threads 0.34 +/- 0.01 seconds Processes 0.16 +/- 0.00 seconds 2.6.12-rc5-fd : Running test 'readwrite' with 8 tasks Threads 0.17 +/- 0.02 seconds Processes 0.17 +/- 0.02 seconds I repeated the measurements on ramfs (as opposed to ext2 on ramdisk in the earlier measurement) and I got more consistent results from tiobench : 4(8) way xeon P4 ----------------- (lock-free) Test 2.6.12-rc5 Stdev 2.6.12-rc5-fd Stdev ------------------------------------------------------------- Seqread 1282 18.59 1343.6 26.37 Randread 1517 7 2415 34.27 Seqwrite 702.2 5.27 709.46 5.9 Randwrite 846.86 15.15 919.68 21.4 4-way ppc64 ------------ (lock-free) Test 2.6.12-rc5 Stdev 2.6.12-rc5-fd Stdev ------------------------------------------------------------- Seqread 1549 91.16 1569.6 47.2 Randread 1473.6 25.11 1585.4 69.99 Seqwrite 1096.8 20.03 1136 29.61 Randwrite 1189.6 4.04 1275.2 32.96 Also running Tridge's thread_perf test on ppc64 : 2.6.12-rc5-vanilla -------------------- Running test 'readwrite' with 4 tasks Threads 0.20 +/- 0.02 seconds Processes 0.16 +/- 0.01 seconds 2.6.12-rc5-fd -------------------- Running test 'readwrite' with 4 tasks Threads 0.18 +/- 0.04 seconds Processes 0.16 +/- 0.01 seconds The benefits are huge (upto ~60%) in some cases on x86 primarily due to the atomic operations during acquisition of ->file_lock and cache line bouncing in fast path. ppc64 benefits are modest due to LL/SC based locking, but still statistically significant. This patch: RCU head initilizer no longer needs the head varible name since we don't use list.h lists anymore. Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] Deprecate synchronize_kernel, GPL replacementPaul E. McKenney2005-05-01
| | | | | | | | | | | | | | | | The synchronize_kernel() primitive is used for quite a few different purposes: waiting for RCU readers, waiting for NMIs, waiting for interrupts, and so on. This makes RCU code harder to read, since synchronize_kernel() might or might not have matching rcu_read_lock()s. This patch creates a new synchronize_rcu() that is to be used for RCU readers and a new synchronize_sched() that is used for the rest. These two new primitives currently have the same implementation, but this is might well change with additional real-time support. Both new primitives are GPL-only, the old primitive is deprecated. Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* Linux-2.6.12-rc2Linus Torvalds2005-04-16
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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