Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753373AbbGNPj7 (ORCPT ); Tue, 14 Jul 2015 11:39:59 -0400 Received: from mail-wi0-f169.google.com ([209.85.212.169]:34491 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751298AbbGNPj5 (ORCPT ); Tue, 14 Jul 2015 11:39:57 -0400 Message-ID: <1436888390.7983.49.camel@gmail.com> Subject: Re: [patch] sched: beef up wake_wide() From: Mike Galbraith To: Peter Zijlstra Cc: Josef Bacik , riel@redhat.com, mingo@redhat.com, linux-kernel@vger.kernel.org, morten.rasmussen@arm.com, kernel-team Date: Tue, 14 Jul 2015 17:39:50 +0200 In-Reply-To: <20150714150455.GM19282@twins.programming.kicks-ass.net> References: <559C0700.6090009@fb.com> <1436336026.3767.53.camel@gmail.com> <20150709132654.GE3644@twins.programming.kicks-ass.net> <1436505566.5715.50.camel@gmail.com> <55A03232.2090500@fb.com> <1436584311.3429.7.camel@gmail.com> <20150714111905.GJ3644@twins.programming.kicks-ass.net> <1436881757.7983.12.camel@gmail.com> <20150714140710.GL19282@twins.programming.kicks-ass.net> <1436883466.7983.17.camel@gmail.com> <20150714150455.GM19282@twins.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.11 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6041 Lines: 189 On Tue, 2015-07-14 at 17:04 +0200, Peter Zijlstra wrote: > On Tue, Jul 14, 2015 at 04:17:46PM +0200, Mike Galbraith wrote: > > There's a buglet, > > > We'll not look for a idle cpu when wake_wide() naks want_affine. > > *sigh* indeed.. fixing that'll bring us very close to what we started > out wiht.. > > The one XXX there raises the question on whether we should always so > select_idle_sibling() if we do not have a suitable balance flag, or only > on wakeups. That's what I've been sitting here waffling over, finally convinced myself that should the user turn FORX/EXEC off, he shouldn't find that a substitute quietly slipped in.. though otoh.. crap, guess I'm not done waffling after all. Yeah, this will work just fine ;-) (typos fixed) --- Subject: sched: Beef up wake_wide() From: Mike Galbraith Date: Fri, 10 Jul 2015 07:19:26 +0200 Josef Bacik reported that Facebook sees better performance with their 1:N load (1 dispatch/node, N workers/node) when carrying an old patch to try very hard to wake to an idle CPU. While looking at wake_wide(), I noticed that it doesn't pay attention to the wakeup of a many partner waker, returning 1 only when waking one of its many partners. Correct that, letting explicit domain flags override the heuristic. While at it, adjust task_struct bits, we don't need a 64bit counter. Cc: morten.rasmussen@arm.com Cc: riel@redhat.com Cc: mingo@redhat.com Signed-off-by: Mike Galbraith Tested-by: Josef Bacik [peterz: frobbings] Signed-off-by: Peter Zijlstra (Intel) Link: http://lkml.kernel.org/r/1436505566.5715.50.camel@gmail.com --- include/linux/sched.h | 4 +- kernel/sched/fair.c | 67 ++++++++++++++++++++++++-------------------------- 2 files changed, 35 insertions(+), 36 deletions(-) --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1351,9 +1351,9 @@ struct task_struct { #ifdef CONFIG_SMP struct llist_node wake_entry; int on_cpu; - struct task_struct *last_wakee; - unsigned long wakee_flips; + unsigned int wakee_flips; unsigned long wakee_flip_decay_ts; + struct task_struct *last_wakee; int wake_cpu; #endif --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4730,26 +4730,29 @@ static long effective_load(struct task_g #endif +/* + * Detect M:N waker/wakee relationships via a switching-frequency heuristic. + * A waker of many should wake a different task than the one last awakened + * at a frequency roughly N times higher than one of its wakees. In order + * to determine whether we should let the load spread vs consolodating to + * shared cache, we look for a minimum 'flip' frequency of llc_size in one + * partner, and a factor of lls_size higher frequency in the other. With + * both conditions met, we can be relatively sure that the relationship is + * non-monogamous, with partner count exceeding socket size. Waker/wakee + * being client/server, worker/dispatcher, interrupt source or whatever is + * irrelevant, spread criteria is apparent partner count exceeds socket size. + */ static int wake_wide(struct task_struct *p) { + unsigned int master = current->wakee_flips; + unsigned int slave = p->wakee_flips; int factor = this_cpu_read(sd_llc_size); - /* - * Yeah, it's the switching-frequency, could means many wakee or - * rapidly switch, use factor here will just help to automatically - * adjust the loose-degree, so bigger node will lead to more pull. - */ - if (p->wakee_flips > factor) { - /* - * wakee is somewhat hot, it needs certain amount of cpu - * resource, so if waker is far more hot, prefer to leave - * it alone. - */ - if (current->wakee_flips > (factor * p->wakee_flips)) - return 1; - } - - return 0; + if (master < slave) + swap(master, slave); + if (slave < factor || master < slave * factor) + return 0; + return 1; } static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) @@ -4761,13 +4764,6 @@ static int wake_affine(struct sched_doma unsigned long weight; int balanced; - /* - * If we wake multiple tasks be careful to not bounce - * ourselves around too much. - */ - if (wake_wide(p)) - return 0; - idx = sd->wake_idx; this_cpu = smp_processor_id(); prev_cpu = task_cpu(p); @@ -5021,17 +5017,17 @@ select_task_rq_fair(struct task_struct * { struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL; int cpu = smp_processor_id(); - int new_cpu = cpu; + int new_cpu = prev_cpu; int want_affine = 0; int sync = wake_flags & WF_SYNC; if (sd_flag & SD_BALANCE_WAKE) - want_affine = cpumask_test_cpu(cpu, tsk_cpus_allowed(p)); + want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, tsk_cpus_allowed(p)); rcu_read_lock(); for_each_domain(cpu, tmp) { if (!(tmp->flags & SD_LOAD_BALANCE)) - continue; + break; /* * If both cpu and prev_cpu are part of this domain, @@ -5045,17 +5041,21 @@ select_task_rq_fair(struct task_struct * if (tmp->flags & sd_flag) sd = tmp; + else if (!want_affine) + break; } - if (affine_sd && cpu != prev_cpu && wake_affine(affine_sd, p, sync)) - prev_cpu = cpu; - - if (sd_flag & SD_BALANCE_WAKE) { - new_cpu = select_idle_sibling(p, prev_cpu); - goto unlock; + if (affine_sd) { + sd = NULL; /* Prefer wake_affine over balance flags */ + if (cpu != prev_cpu && wake_affine(affine_sd, p, sync)) + new_cpu = cpu; } - while (sd) { + if (!sd) { + if (sd_flag & SD_BALANCE_WAKE) /* XXX always ? */ + new_cpu = select_idle_sibling(p, new_cpu); + + } else while (sd) { struct sched_group *group; int weight; @@ -5089,7 +5089,6 @@ select_task_rq_fair(struct task_struct * } /* while loop will break here if sd == NULL */ } -unlock: rcu_read_unlock(); return new_cpu; -- 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/