Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752678AbXIMLYl (ORCPT ); Thu, 13 Sep 2007 07:24:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750966AbXIMLYd (ORCPT ); Thu, 13 Sep 2007 07:24:33 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:34192 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750892AbXIMLYb (ORCPT ); Thu, 13 Sep 2007 07:24:31 -0400 Date: Thu, 13 Sep 2007 13:24:27 +0200 From: Ingo Molnar To: Antoine Martin Cc: Linux Kernel Development Subject: Re: CFS: some bad numbers with Java/database threading Message-ID: <20070913112427.GA20686@elte.hu> References: <46E871FE.9010908@nagafix.co.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <46E871FE.9010908@nagafix.co.uk> User-Agent: Mutt/1.5.14 (2007-02-12) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.1.7-deb -1.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5948 Lines: 196 * Antoine Martin wrote: > Basically, all the previous kernels are pretty close (2.6.16 through > to 2.6.20 performed almost identically to 2.6.22 and are not shown > here to avoid cluttering the graphs) > > All the 2.6.23-rc kernels performed poorly (except -rc3!): much more > erratically and with a sharp performance drop above 800 threads. The > load starts to go up and the performance takes a nosedive. hm, could you try the patch below ontop of 2.6.23-rc6 and do: echo 1 > /proc/sys/kernel/sched_yield_bug_workaround does this improve the numbers? Ingo --------------> Subject: sched: yield debugging From: Ingo Molnar introduce various sched_yield implementations: # default one: echo 0 > /proc/sys/kernel/sched_yield_bug_workaround # always queues the current task next to the next task: echo 1 > /proc/sys/kernel/sched_yield_bug_workaround # NOP: echo 2 > /proc/sys/kernel/sched_yield_bug_workaround tunability depends on CONFIG_SCHED_DEBUG=y. Not-yet-signed-off-by: Ingo Molnar --- include/linux/sched.h | 2 + kernel/sched_fair.c | 73 +++++++++++++++++++++++++++++++++++++++++++++----- kernel/sysctl.c | 19 +++++++++++++ 3 files changed, 88 insertions(+), 6 deletions(-) Index: linux/include/linux/sched.h =================================================================== --- linux.orig/include/linux/sched.h +++ linux/include/linux/sched.h @@ -1392,10 +1392,12 @@ extern void sched_idle_next(void); #ifdef CONFIG_SCHED_DEBUG extern unsigned int sysctl_sched_latency; extern unsigned int sysctl_sched_min_granularity; +extern unsigned int sysctl_sched_yield_granularity; extern unsigned int sysctl_sched_wakeup_granularity; extern unsigned int sysctl_sched_batch_wakeup_granularity; extern unsigned int sysctl_sched_stat_granularity; extern unsigned int sysctl_sched_runtime_limit; +extern unsigned int sysctl_sched_yield_bug_workaround; extern unsigned int sysctl_sched_child_runs_first; extern unsigned int sysctl_sched_features; #endif Index: linux/kernel/sched_fair.c =================================================================== --- linux.orig/kernel/sched_fair.c +++ linux/kernel/sched_fair.c @@ -42,6 +42,16 @@ const_debug unsigned int sysctl_sched_la */ const_debug unsigned int sysctl_sched_child_runs_first = 1; +const_debug unsigned int sysctl_sched_yield_granularity = 10000000ULL; + +/* + * sys_sched_yield workaround switch. + * + * This option switches the yield implementation of the + * old scheduler back on. + */ +const_debug unsigned int sysctl_sched_yield_bug_workaround; + /* * Minimal preemption granularity for CPU-bound tasks: * (default: 2 msec, units: nanoseconds) @@ -675,15 +685,66 @@ static void dequeue_task_fair(struct rq */ static void yield_task_fair(struct rq *rq, struct task_struct *p) { - struct cfs_rq *cfs_rq = task_cfs_rq(p); + if (!sysctl_sched_yield_bug_workaround) { + struct cfs_rq *cfs_rq = task_cfs_rq(p); + __update_rq_clock(rq); + + /* + * Dequeue and enqueue the task to update its + * position within the tree: + */ + dequeue_entity(cfs_rq, &p->se, 0); + enqueue_entity(cfs_rq, &p->se, 0); + return; + } + + if (sysctl_sched_yield_bug_workaround == 1) { + struct cfs_rq *cfs_rq = task_cfs_rq(p); + struct rb_node *curr, *next, *first; + struct task_struct *p_next; + s64 yield_key; + + __update_rq_clock(rq); + curr = &p->se.run_node; + first = first_fair(cfs_rq); + /* + * Move this task to the second place in the tree: + */ + if (unlikely(curr != first)) { + next = first; + } else { + next = rb_next(curr); + /* + * We were the last one already - nothing to do, return + * and reschedule: + */ + if (unlikely(!next)) + return; + } + + p_next = rb_entry(next, struct task_struct, se.run_node); + /* + * Minimally necessary key value to be the second in the tree: + */ + yield_key = p_next->se.fair_key + (int)sysctl_sched_yield_granularity; + + dequeue_entity(cfs_rq, &p->se, 0); + + /* + * Only update the key if we need to move more backwards + * than the minimally necessary position to be the second: + */ + if (p->se.fair_key < yield_key) + p->se.fair_key = yield_key; + + __enqueue_entity(cfs_rq, &p->se); + return; + } - __update_rq_clock(rq); /* - * Dequeue and enqueue the task to update its - * position within the tree: + * Just reschedule, do nothing else: */ - dequeue_entity(cfs_rq, &p->se, 0); - enqueue_entity(cfs_rq, &p->se, 0); + resched_task(p); } /* Index: linux/kernel/sysctl.c =================================================================== --- linux.orig/kernel/sysctl.c +++ linux/kernel/sysctl.c @@ -244,6 +244,17 @@ static ctl_table kern_table[] = { }, { .ctl_name = CTL_UNNUMBERED, + .procname = "sched_yield_granularity_ns", + .data = &sysctl_sched_yield_granularity, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = &proc_dointvec_minmax, + .strategy = &sysctl_intvec, + .extra1 = &min_sched_granularity_ns, + .extra2 = &max_sched_granularity_ns, + }, + { + .ctl_name = CTL_UNNUMBERED, .procname = "sched_wakeup_granularity_ns", .data = &sysctl_sched_wakeup_granularity, .maxlen = sizeof(unsigned int), @@ -266,6 +277,14 @@ static ctl_table kern_table[] = { }, { .ctl_name = CTL_UNNUMBERED, + .procname = "sched_yield_bug_workaround", + .data = &sysctl_sched_yield_bug_workaround, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = &proc_dointvec, + }, + { + .ctl_name = CTL_UNNUMBERED, .procname = "sched_child_runs_first", .data = &sysctl_sched_child_runs_first, .maxlen = sizeof(unsigned int), - 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/