From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755488AbaEHSrv (ORCPT ); Thu, 8 May 2014 14:47:51 -0400 Received: from mail-ob0-f171.google.com ([209.85.214.171]:61820 "EHLO mail-ob0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755467AbaEHSru (ORCPT ); Thu, 8 May 2014 14:47:50 -0400 From: minyard@acm.org To: Ingo Molnar , Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Corey Minyard Subject: [PATCH] sched: Initialize rq->age_stamp on processor start Date: Thu, 8 May 2014 13:47:39 -0500 Message-Id: <1399574859-11714-1-git-send-email-minyard@acm.org> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <20140508161337.GF30445@twins.programming.kicks-ass.net> References: <20140508161337.GF30445@twins.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Corey Minyard If the sched_clock time starts at a large value, the kernel will spin in sched_avg_update for a long time while rq->age_stamp catches up with rq->clock. The comment in kernel/sched/clock.c says that there is no strict promise that it starts at zero. So initialize rq->age_stamp when a cpu starts up to avoid this. I was seeing long delays on a simulator that didn't start the clock at zero. This might also be an issue on reboots on processors that don't re-initialize the timer to zero on reset, and when using kexec. Signed-off-by: Corey Minyard --- kernel/sched/core.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 268a45e..80725c9 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5039,11 +5039,20 @@ static struct notifier_block migration_notifier = { .priority = CPU_PRI_MIGRATION, }; +static void __cpuinit set_cpu_rq_start_time(void) +{ + int cpu = smp_processor_id(); + struct rq *rq = cpu_rq(cpu); + rq->age_stamp = sched_clock_cpu(cpu); +} + static int sched_cpu_active(struct notifier_block *nfb, unsigned long action, void *hcpu) { switch (action & ~CPU_TASKS_FROZEN) { case CPU_STARTING: + set_cpu_rq_start_time(); + /* fall through */ case CPU_DOWN_FAILED: set_cpu_active((long)hcpu, true); return NOTIFY_OK; @@ -6919,6 +6928,7 @@ void __init sched_init(void) if (cpu_isolated_map == NULL) zalloc_cpumask_var(&cpu_isolated_map, GFP_NOWAIT); idle_thread_set_boot_cpu(); + set_cpu_rq_start_time(); #endif init_sched_fair_class(); -- 1.8.3.1