From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753017AbaCRAGB (ORCPT ); Mon, 17 Mar 2014 20:06:01 -0400 Received: from mail-ob0-f178.google.com ([209.85.214.178]:53829 "EHLO mail-ob0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752841AbaCRAF7 (ORCPT ); Mon, 17 Mar 2014 20:05:59 -0400 From: minyard@acm.org To: linux-kernel@vger.kernel.org Cc: Corey Minyard Subject: [PATCH] sched: Initialize rq->age_stamp on processor start Date: Mon, 17 Mar 2014 19:05:49 -0500 Message-Id: <1395101149-10097-1-git-send-email-minyard@acm.org> X-Mailer: git-send-email 1.8.3.1 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 b46131e..5be3d4a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5037,11 +5037,20 @@ 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; @@ -6922,6 +6931,7 @@ void __init sched_init(void) init_sched_fair_class(); scheduler_running = 1; + set_cpu_rq_start_time(); } #ifdef CONFIG_DEBUG_ATOMIC_SLEEP -- 1.8.3.1