Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752419AbbHCIoW (ORCPT ); Mon, 3 Aug 2015 04:44:22 -0400 Received: from mail-la0-f42.google.com ([209.85.215.42]:34360 "EHLO mail-la0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751629AbbHCIoV (ORCPT ); Mon, 3 Aug 2015 04:44:21 -0400 MIME-Version: 1.0 In-Reply-To: <1438380767.7608.11.camel@j-VirtualBox> References: <1438336149-25809-1-git-send-email-vincent.guittot@linaro.org> <1438380767.7608.11.camel@j-VirtualBox> From: Vincent Guittot Date: Mon, 3 Aug 2015 10:44:00 +0200 Message-ID: Subject: Re: [PATCH] sched: fix nohz.next_balance update To: Jason Low Cc: Peter Zijlstra , Ingo Molnar , linux-kernel , Preeti U Murthy , Linaro Kernel Mailman List Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2865 Lines: 68 Hi Jason, On 1 August 2015 at 00:12, Jason Low wrote: > Hi Vincent, > > On Fri, 2015-07-31 at 11:49 +0200, Vincent Guittot wrote: >> Since commit d4573c3e1c99 ("sched: Improve load balancing in the presence >> of idle CPUs"), the ILB CPU starts with the idle load balancing of other >> idle CPUs and finishes with itself in order to speed up the spread of tasks >> in all idle CPUs. >> >> The this_rq->next_balance is still used in nohz_idle_balance as an >> intermediate step to gather the shortest next balance before updating >> nohz.next_balance. But the former has not been updated yet and is likely to >> be set with the current jiffies. As a result, the nohz.next_balance will be >> set with current jiffies instead of the real next balance date. This >> generates spurious kicks of nohz ilde balance. >> >> nohz_idle_balance must set the nohz.next_balance without taking into >> account this_rq->next_balance which is not updated yet. Then, this_rq will >> update nohz.next_update with its next_balance once updated and if necessary. >> >> Signed-off-by: Vincent Guittot >> --- >> kernel/sched/fair.c | 33 +++++++++++++++++++++++++++++---- >> 1 file changed, 29 insertions(+), 4 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 587a2f6..2b02089 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -7779,8 +7779,21 @@ static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle) >> * When the cpu is attached to null domain for ex, it will not be >> * updated. >> */ >> - if (likely(update_next_balance)) >> + if (likely(update_next_balance)) { >> rq->next_balance = next_balance; >> + >> + /* >> + * If this cpu has been elected to perform the nohz idle >> + * balance. Other idle cpus have already rebalance with >> + * nohz_idle_balance and the nohz.next_balaance has been >> + * updated accordingly. This cpu has now run the idle load >> + * balance for itself and we need to update the >> + * nohz.next_balance accordingly. >> + */ >> + if ((idle == CPU_IDLE) && >> + time_after(nohz.next_balance, rq->next_balance)) >> + nohz.next_balance = rq->next_balance; > > The code accessing the "nohz" structure may also need to be put in an: > > #ifdef CONFIG_NO_HZ_COMMON > > in order for it to compile when !CONFIG_NO_HZ_COMMON. You're right. I'm going to fix that right now Vincent > -- 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/