Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755115Ab1FOUNd (ORCPT ); Wed, 15 Jun 2011 16:13:33 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:55563 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752013Ab1FOUNc (ORCPT ); Wed, 15 Jun 2011 16:13:32 -0400 Date: Wed, 15 Jun 2011 22:12:16 +0200 From: Ingo Molnar To: Linus Torvalds Cc: Peter Zijlstra , Paul McKenney , Tim Chen , Andrew Morton , Hugh Dickins , KOSAKI Motohiro , Benjamin Herrenschmidt , David Miller , Martin Schwidefsky , Russell King , Paul Mundt , Jeff Dike , Richard Weinberger , Tony Luck , KAMEZAWA Hiroyuki , Mel Gorman , Nick Piggin , Namhyung Kim , ak@linux.intel.com, shaohua.li@intel.com, alex.shi@intel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, "Rafael J. Wysocki" Subject: [GIT PULL] Re: REGRESSION: Performance regressions from switching anon_vma->lock to mutex Message-ID: <20110615201216.GA4762@elte.hu> References: <1308097798.17300.142.camel@schen9-DESK> <1308134200.15315.32.camel@twins> <1308135495.15315.38.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 12846 Lines: 389 * Linus Torvalds wrote: > On Wed, Jun 15, 2011 at 3:58 AM, Peter Zijlstra wrote: > > > > The first thing that stood out when running it was: > > > > 31694 root ? ? ?20 ? 0 26660 1460 1212 S 17.5 ?0.0 ? 0:01.97 exim > > ? ?7 root ? ? ?-2 ?19 ? ? 0 ? ?0 ? ?0 S 12.7 ?0.0 ? 0:06.14 rcuc0 > ... > > > > Which is an impressive amount of RCU usage.. > > Gaah. Can we just revert that crazy "use threads for RCU" thing already? I have this fix queued up currently: 09223371deac: rcu: Use softirq to address performance regression and that's ready for pulling and should fix this regression: git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git core-urgent-for-linus The revert itself looks quite hairy, i just attempted it: it affects half a dozen other followup commits. We might be better off using the (tested) commit above and then shutting down all kthread based processing and always use a softirq ... or something like that. if you think that's risky and we should do the revert then i'll rebase the core/urgent branch and we'll do the revert. Paul, Peter, what do you think? Thanks, Ingo ------------------> Paul E. McKenney (1): rcu: Simplify curing of load woes Shaohua Li (1): rcu: Use softirq to address performance regression Documentation/filesystems/proc.txt | 1 + include/linux/interrupt.h | 1 + include/trace/events/irq.h | 3 +- kernel/rcutree.c | 88 ++++++++++++++++------------------- kernel/rcutree.h | 1 + kernel/rcutree_plugin.h | 20 ++++---- kernel/softirq.c | 2 +- tools/perf/util/trace-event-parse.c | 1 + 8 files changed, 57 insertions(+), 60 deletions(-) diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index f481780..db3b1ab 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -843,6 +843,7 @@ Provides counts of softirq handlers serviced since boot time, for each cpu. TASKLET: 0 0 0 290 SCHED: 27035 26983 26971 26746 HRTIMER: 0 0 0 0 + RCU: 1678 1769 2178 2250 1.3 IDE devices in /proc/ide diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index 6c12989..f6efed0 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -414,6 +414,7 @@ enum TASKLET_SOFTIRQ, SCHED_SOFTIRQ, HRTIMER_SOFTIRQ, + RCU_SOFTIRQ, /* Preferable RCU should always be the last softirq */ NR_SOFTIRQS }; diff --git a/include/trace/events/irq.h b/include/trace/events/irq.h index ae045ca..1c09820 100644 --- a/include/trace/events/irq.h +++ b/include/trace/events/irq.h @@ -20,7 +20,8 @@ struct softirq_action; softirq_name(BLOCK_IOPOLL), \ softirq_name(TASKLET), \ softirq_name(SCHED), \ - softirq_name(HRTIMER)) + softirq_name(HRTIMER), \ + softirq_name(RCU)) /** * irq_handler_entry - called immediately before the irq action handler diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 89419ff..ae5c9ea 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -100,6 +100,7 @@ static char rcu_kthreads_spawnable; static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu); static void invoke_rcu_cpu_kthread(void); +static void __invoke_rcu_cpu_kthread(void); #define RCU_KTHREAD_PRIO 1 /* RT priority for per-CPU kthreads. */ @@ -1442,13 +1443,21 @@ __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp) } /* If there are callbacks ready, invoke them. */ - rcu_do_batch(rsp, rdp); + if (cpu_has_callbacks_ready_to_invoke(rdp)) + __invoke_rcu_cpu_kthread(); +} + +static void rcu_kthread_do_work(void) +{ + rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data)); + rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); + rcu_preempt_do_callbacks(); } /* * Do softirq processing for the current CPU. */ -static void rcu_process_callbacks(void) +static void rcu_process_callbacks(struct softirq_action *unused) { __rcu_process_callbacks(&rcu_sched_state, &__get_cpu_var(rcu_sched_data)); @@ -1465,7 +1474,7 @@ static void rcu_process_callbacks(void) * the current CPU with interrupts disabled, the rcu_cpu_kthread_task * cannot disappear out from under us. */ -static void invoke_rcu_cpu_kthread(void) +static void __invoke_rcu_cpu_kthread(void) { unsigned long flags; @@ -1479,6 +1488,11 @@ static void invoke_rcu_cpu_kthread(void) local_irq_restore(flags); } +static void invoke_rcu_cpu_kthread(void) +{ + raise_softirq(RCU_SOFTIRQ); +} + /* * Wake up the specified per-rcu_node-structure kthread. * Because the per-rcu_node kthreads are immortal, we don't need @@ -1613,7 +1627,7 @@ static int rcu_cpu_kthread(void *arg) *workp = 0; local_irq_restore(flags); if (work) - rcu_process_callbacks(); + rcu_kthread_do_work(); local_bh_enable(); if (*workp != 0) spincnt++; @@ -1635,6 +1649,20 @@ static int rcu_cpu_kthread(void *arg) * to manipulate rcu_cpu_kthread_task. There might be another CPU * attempting to access it during boot, but the locking in kthread_bind() * will enforce sufficient ordering. + * + * Please note that we cannot simply refuse to wake up the per-CPU + * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state, + * which can result in softlockup complaints if the task ends up being + * idle for more than a couple of minutes. + * + * However, please note also that we cannot bind the per-CPU kthread to its + * CPU until that CPU is fully online. We also cannot wait until the + * CPU is fully online before we create its per-CPU kthread, as this would + * deadlock the system when CPU notifiers tried waiting for grace + * periods. So we bind the per-CPU kthread to its CPU only if the CPU + * is online. If its CPU is not yet fully online, then the code in + * rcu_cpu_kthread() will wait until it is fully online, and then do + * the binding. */ static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu) { @@ -1647,12 +1675,14 @@ static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu) t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu); if (IS_ERR(t)) return PTR_ERR(t); - kthread_bind(t, cpu); + if (cpu_online(cpu)) + kthread_bind(t, cpu); per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu; WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL); - per_cpu(rcu_cpu_kthread_task, cpu) = t; sp.sched_priority = RCU_KTHREAD_PRIO; sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); + per_cpu(rcu_cpu_kthread_task, cpu) = t; + wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */ return 0; } @@ -1759,12 +1789,11 @@ static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp, raw_spin_unlock_irqrestore(&rnp->lock, flags); sp.sched_priority = 99; sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); + wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ } return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index); } -static void rcu_wake_one_boost_kthread(struct rcu_node *rnp); - /* * Spawn all kthreads -- called as soon as the scheduler is running. */ @@ -1772,30 +1801,18 @@ static int __init rcu_spawn_kthreads(void) { int cpu; struct rcu_node *rnp; - struct task_struct *t; rcu_kthreads_spawnable = 1; for_each_possible_cpu(cpu) { per_cpu(rcu_cpu_has_work, cpu) = 0; - if (cpu_online(cpu)) { + if (cpu_online(cpu)) (void)rcu_spawn_one_cpu_kthread(cpu); - t = per_cpu(rcu_cpu_kthread_task, cpu); - if (t) - wake_up_process(t); - } } rnp = rcu_get_root(rcu_state); (void)rcu_spawn_one_node_kthread(rcu_state, rnp); - if (rnp->node_kthread_task) - wake_up_process(rnp->node_kthread_task); if (NUM_RCU_NODES > 1) { - rcu_for_each_leaf_node(rcu_state, rnp) { + rcu_for_each_leaf_node(rcu_state, rnp) (void)rcu_spawn_one_node_kthread(rcu_state, rnp); - t = rnp->node_kthread_task; - if (t) - wake_up_process(t); - rcu_wake_one_boost_kthread(rnp); - } } return 0; } @@ -2221,31 +2238,6 @@ static void __cpuinit rcu_prepare_kthreads(int cpu) } /* - * kthread_create() creates threads in TASK_UNINTERRUPTIBLE state, - * but the RCU threads are woken on demand, and if demand is low this - * could be a while triggering the hung task watchdog. - * - * In order to avoid this, poke all tasks once the CPU is fully - * up and running. - */ -static void __cpuinit rcu_online_kthreads(int cpu) -{ - struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu); - struct rcu_node *rnp = rdp->mynode; - struct task_struct *t; - - t = per_cpu(rcu_cpu_kthread_task, cpu); - if (t) - wake_up_process(t); - - t = rnp->node_kthread_task; - if (t) - wake_up_process(t); - - rcu_wake_one_boost_kthread(rnp); -} - -/* * Handle CPU online/offline notification events. */ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, @@ -2262,7 +2254,6 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, rcu_prepare_kthreads(cpu); break; case CPU_ONLINE: - rcu_online_kthreads(cpu); case CPU_DOWN_FAILED: rcu_node_kthread_setaffinity(rnp, -1); rcu_cpu_kthread_setrt(cpu, 1); @@ -2410,6 +2401,7 @@ void __init rcu_init(void) rcu_init_one(&rcu_sched_state, &rcu_sched_data); rcu_init_one(&rcu_bh_state, &rcu_bh_data); __rcu_init_preempt(); + open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); /* * We don't need protection against CPU-hotplug here because diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 7b9a08b..0fed6b9 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -439,6 +439,7 @@ static void rcu_preempt_offline_cpu(int cpu); #endif /* #ifdef CONFIG_HOTPLUG_CPU */ static void rcu_preempt_check_callbacks(int cpu); static void rcu_preempt_process_callbacks(void); +static void rcu_preempt_do_callbacks(void); void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)); #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU) static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp); diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index c8bff30..38d09c5 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -602,6 +602,11 @@ static void rcu_preempt_process_callbacks(void) &__get_cpu_var(rcu_preempt_data)); } +static void rcu_preempt_do_callbacks(void) +{ + rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data)); +} + /* * Queue a preemptible-RCU callback for invocation after a grace period. */ @@ -997,6 +1002,10 @@ static void rcu_preempt_process_callbacks(void) { } +static void rcu_preempt_do_callbacks(void) +{ +} + /* * Wait for an rcu-preempt grace period, but make it happen quickly. * But because preemptible RCU does not exist, map to rcu-sched. @@ -1299,15 +1308,10 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, raw_spin_unlock_irqrestore(&rnp->lock, flags); sp.sched_priority = RCU_KTHREAD_PRIO; sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); + wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ return 0; } -static void __cpuinit rcu_wake_one_boost_kthread(struct rcu_node *rnp) -{ - if (rnp->boost_kthread_task) - wake_up_process(rnp->boost_kthread_task); -} - #else /* #ifdef CONFIG_RCU_BOOST */ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) @@ -1331,10 +1335,6 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, return 0; } -static void __cpuinit rcu_wake_one_boost_kthread(struct rcu_node *rnp) -{ -} - #endif /* #else #ifdef CONFIG_RCU_BOOST */ #ifndef CONFIG_SMP diff --git a/kernel/softirq.c b/kernel/softirq.c index 1396017..40cf63d 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -58,7 +58,7 @@ DEFINE_PER_CPU(struct task_struct *, ksoftirqd); char *softirq_to_name[NR_SOFTIRQS] = { "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL", - "TASKLET", "SCHED", "HRTIMER" + "TASKLET", "SCHED", "HRTIMER", "RCU" }; /* diff --git a/tools/perf/util/trace-event-parse.c b/tools/perf/util/trace-event-parse.c index 1e88485..0a7ed5b 100644 --- a/tools/perf/util/trace-event-parse.c +++ b/tools/perf/util/trace-event-parse.c @@ -2187,6 +2187,7 @@ static const struct flag flags[] = { { "TASKLET_SOFTIRQ", 6 }, { "SCHED_SOFTIRQ", 7 }, { "HRTIMER_SOFTIRQ", 8 }, + { "RCU_SOFTIRQ", 9 }, { "HRTIMER_NORESTART", 0 }, { "HRTIMER_RESTART", 1 }, -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/