From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752876Ab3BUI3d (ORCPT ); Thu, 21 Feb 2013 03:29:33 -0500 Received: from mail-wi0-f170.google.com ([209.85.212.170]:63388 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752617Ab3BUI3b (ORCPT ); Thu, 21 Feb 2013 03:29:31 -0500 From: Vincent Guittot To: linux-kernel@vger.kernel.org, linaro-dev@lists.linaro.org, peterz@infradead.org, mingo@kernel.org, fweisbec@gmail.com, rostedt@goodmis.org, efault@gmx.de Cc: Vincent Guittot Subject: [PATCH v4] sched: fix init NOHZ_IDLE flag Date: Thu, 21 Feb 2013 09:29:16 +0100 Message-Id: <1361435356-28466-1-git-send-email-vincent.guittot@linaro.org> X-Mailer: git-send-email 1.7.9.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On my smp platform which is made of 5 cores in 2 clusters, I have the nr_busy_cpu field of sched_group_power struct that is not null when the platform is fully idle. The root cause seems to be: During the boot sequence, some CPUs reach the idle loop and set their NOHZ_IDLE flag while waiting for others CPUs to boot. But the nr_busy_cpus field is initialized later with the assumption that all CPUs are in the busy state whereas some CPUs have already set their NOHZ_IDLE flag. During the initialization of the sched_domain, we set the NOHZ_IDLE flag when nr_busy_cpus is initialized to 0 in order to have a coherent configuration. If a CPU enters idle and call set_cpu_sd_state_idle during the build of the new sched_domain it will not corrupt the initial state set_cpu_sd_state_busy is modified and clears the NOHZ_IDLE only if a non NULL sched_domain is attached to the CPU (which is the case during the rebuild) Change since V3; - NOHZ flag is not cleared if a NULL domain is attached to the CPU - Remove patch 2/2 which becomes useless with latest modifications Change since V2: - change the initialization to idle state instead of busy state so a CPU that enters idle during the build of the sched_domain will not corrupt the initialization state Change since V1: - remove the patch for SCHED softirq on an idle core use case as it was a side effect of the other use cases. Signed-off-by: Vincent Guittot --- kernel/sched/core.c | 4 +++- kernel/sched/fair.c | 9 +++++++-- 2 files changed, 10 insertions(+), 3 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 26058d0..c730a4e 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5884,7 +5884,9 @@ static void init_sched_groups_power(int cpu, struct sched_domain *sd) return; update_group_power(sd, cpu); - atomic_set(&sg->sgp->nr_busy_cpus, sg->group_weight); + atomic_set(&sg->sgp->nr_busy_cpus, 0); + set_bit(NOHZ_IDLE, nohz_flags(cpu)); + } int __weak arch_sd_sibling_asym_packing(void) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 81fa536..2701a92 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5403,15 +5403,20 @@ static inline void set_cpu_sd_state_busy(void) { struct sched_domain *sd; int cpu = smp_processor_id(); + int clear = 0; if (!test_bit(NOHZ_IDLE, nohz_flags(cpu))) return; - clear_bit(NOHZ_IDLE, nohz_flags(cpu)); rcu_read_lock(); - for_each_domain(cpu, sd) + for_each_domain(cpu, sd) { atomic_inc(&sd->groups->sgp->nr_busy_cpus); + clear = 1; + } rcu_read_unlock(); + + if (likely(clear)) + clear_bit(NOHZ_IDLE, nohz_flags(cpu)); } void set_cpu_sd_state_idle(void) -- 1.7.9.5