Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751493Ab3HTScS (ORCPT ); Tue, 20 Aug 2013 14:32:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:13493 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751184Ab3HTScR (ORCPT ); Tue, 20 Aug 2013 14:32:17 -0400 Date: Tue, 20 Aug 2013 20:25:53 +0200 From: Oleg Nesterov To: Peter Zijlstra Cc: Arjan van de Ven , Fernando Luis =?iso-8859-1?Q?V=E1zquez?= Cao , Frederic Weisbecker , Ingo Molnar , Thomas Gleixner , LKML , Tetsuo Handa , Andrew Morton Subject: Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock Message-ID: <20130820182553.GB22287@redhat.com> References: <20130816162056.GE24210@somewhere> <20130816162654.GA453@redhat.com> <20130816164626.GH24210@somewhere> <20130819111026.GE24092@twins.programming.kicks-ass.net> <521313D8.9080500@lab.ntt.co.jp> <20130820084405.GC3258@twins.programming.kicks-ass.net> <52138BE9.5090005@linux.intel.com> <20130820160146.GG3258@twins.programming.kicks-ass.net> <20130820163312.GA17957@redhat.com> <20130820175429.GI3258@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130820175429.GI3258@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2028 Lines: 74 On 08/20, Peter Zijlstra wrote: > > On Tue, Aug 20, 2013 at 06:33:12PM +0200, Oleg Nesterov wrote: > > --- x/kernel/sched/core.c > > +++ x/kernel/sched/core.c > > @@ -2435,6 +2435,9 @@ need_resched: > > rq->curr = next; > > ++*switch_count; > > > > + if (unlikely(prev->in_iowait)) > > + rq->nr_iowait++; > > + > > context_switch(rq, prev, next); /* unlocks the rq */ > > /* > > * The context switch have flipped the stack from under us > > @@ -2442,6 +2445,12 @@ need_resched: > > * this task called schedule() in the past. prev == current > > * is still correct, but it can be moved to another cpu/rq. > > */ > > + if (unlikely(prev->in_iowait)) { > > + raw_spin_lock_irq(&rq->lock); > > + rq->nr_iowait--; > > + raw_spin_unlock_irq(&rq->lock); > > + } > > This seems like the wrong place, this is where you return from > schedule() running another task, Yes, but prev is current, and rq should be "correct" for rq->nr_iowait-- ? This local var should be equal to its value when this task called context_switch() in the past. Like any other variable, like "rq = raw_rq()" in io_schedule(). > not where the task you just send to > sleep wakes up. sure, but currently io_schedule() does the same. Btw. Whatever we do, can't we unify io_schedule/io_schedule_timeout? Oleg. --- x/kernel/sched/core.c +++ x/kernel/sched/core.c @@ -3939,16 +3939,7 @@ EXPORT_SYMBOL_GPL(yield_to); */ void __sched io_schedule(void) { - struct rq *rq = raw_rq(); - - delayacct_blkio_start(); - atomic_inc(&rq->nr_iowait); - blk_flush_plug(current); - current->in_iowait = 1; - schedule(); - current->in_iowait = 0; - atomic_dec(&rq->nr_iowait); - delayacct_blkio_end(); + io_schedule_timeout(MAX_SCHEDULE_TIMEOUT); } EXPORT_SYMBOL(io_schedule); -- 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/