Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753089Ab3FDK02 (ORCPT ); Tue, 4 Jun 2013 06:26:28 -0400 Received: from mail-ea0-f179.google.com ([209.85.215.179]:50904 "EHLO mail-ea0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751281Ab3FDK00 (ORCPT ); Tue, 4 Jun 2013 06:26:26 -0400 Date: Tue, 4 Jun 2013 12:26:22 +0200 From: Frederic Weisbecker To: Peter Zijlstra Cc: Vincent Guittot , linux-kernel , "linaro-kernel@lists.linaro.org" , Ingo Molnar Subject: Re: [PATCH] sched: fix clear NOHZ_BALANCE_KICK Message-ID: <20130604102620.GB14012@somewhere> References: <1369927385-7801-1-git-send-email-vincent.guittot@linaro.org> <20130603224836.GA9388@somewhere> <20130604093611.GJ8923@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130604093611.GJ8923@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4414 Lines: 146 On Tue, Jun 04, 2013 at 11:36:11AM +0200, Peter Zijlstra wrote: > > The best I can seem to come up with is something like the below; but I think > its ghastly. Surely we can do something saner with that bit. > > Having to clear it at 3 different places is just wrong. We could clear the flag early in scheduler_ipi() and set some specific value in rq->idle_balance that tells we want nohz idle balancing from the softirq, something like this untested: diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 58453b8..330136b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -630,15 +630,14 @@ void wake_up_nohz_cpu(int cpu) wake_up_idle_cpu(cpu); } -static inline bool got_nohz_idle_kick(void) +static inline bool got_nohz_idle_kick(int cpu) { - int cpu = smp_processor_id(); - return idle_cpu(cpu) && test_bit(NOHZ_BALANCE_KICK, nohz_flags(cpu)); + return test_and_clear_bit(NOHZ_BALANCE_KICK, nohz_flags(cpu)); } #else /* CONFIG_NO_HZ_COMMON */ -static inline bool got_nohz_idle_kick(void) +static inline bool got_nohz_idle_kick(int cpu) { return false; } @@ -1393,8 +1392,12 @@ static void sched_ttwu_pending(void) void scheduler_ipi(void) { - if (llist_empty(&this_rq()->wake_list) && !got_nohz_idle_kick() - && !tick_nohz_full_cpu(smp_processor_id())) + int cpu = smp_processor_id(); + bool idle_kick = got_nohz_idle_kick(cpu); + + if (!(idle_kick && idle_cpu(cpu)) + && llist_empty(&this_rq()->wake_list) + && !tick_nohz_full_cpu(cpu) return; /* @@ -1417,8 +1420,8 @@ void scheduler_ipi(void) /* * Check if someone kicked us for doing the nohz idle load balance. */ - if (unlikely(got_nohz_idle_kick() && !need_resched())) { - this_rq()->idle_balance = 1; + if (unlikely(idle_kick && idle_cpu(cpu) && !need_resched())) { + this_rq()->idle_balance = IDLE_NOHZ_BALANCE; raise_softirq_irqoff(SCHED_SOFTIRQ); } irq_exit(); diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index c61a614..816e7b0 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5577,15 +5577,14 @@ out: * In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the * rebalancing for all the cpus for whom scheduler ticks are stopped. */ -static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle) +static void nohz_idle_balance(int this_cpu) { struct rq *this_rq = cpu_rq(this_cpu); struct rq *rq; int balance_cpu; - if (idle != CPU_IDLE || - !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu))) - goto end; + if (this_rq->idle_balance != IDLE_NOHZ_BALANCE) + return; for_each_cpu(balance_cpu, nohz.idle_cpus_mask) { if (balance_cpu == this_cpu || !idle_cpu(balance_cpu)) @@ -5612,8 +5611,12 @@ static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle) this_rq->next_balance = rq->next_balance; } nohz.next_balance = this_rq->next_balance; -end: - clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)); + + /* There could be concurrent updates from irqs but we don't care */ + if (idle_cpu(this_cpu)) + this_rq->idle_balance = IDLE_BALANCE; + else + this_rq->idle_balance = 0; } /* @@ -5679,7 +5682,7 @@ need_kick: return 1; } #else -static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle) { } +static void nohz_idle_balance(int this_cpu) { } #endif /* @@ -5700,7 +5703,7 @@ static void run_rebalance_domains(struct softirq_action *h) * balancing on behalf of the other idle cpus whose ticks are * stopped. */ - nohz_idle_balance(this_cpu, idle); + nohz_idle_balance(this_cpu); } static inline int on_null_domain(int cpu) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index ce39224..e9de976 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -387,6 +387,11 @@ extern struct root_domain def_root_domain; #endif /* CONFIG_SMP */ +enum idle_balance_type { + IDLE_BALANCE = 1, + IDLE_NOHZ_BALANCE = 2, +}; + /* * This is the main, per-CPU runqueue data structure. * @@ -458,7 +463,7 @@ struct rq { unsigned long cpu_power; - unsigned char idle_balance; + enum idle_balance_type idle_balance; /* For active balancing */ int post_schedule; int active_balance; -- 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/