From: Pavan Kondeti Subject: Re: [PATCH 1/4] sched: move IO scheduling accounting from io_schedule_timeout() to __schedule() Date: Thu, 3 Nov 2016 21:03:45 +0530 Message-ID: References: <1477673892-28940-1-git-send-email-tj@kernel.org> <1477673892-28940-2-git-send-email-tj@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, mingo@redhat.com, Peter Zijlstra , axboe@kernel.dk, tytso@mit.edu, jack@suse.com, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, mingbo@fb.com To: Tejun Heo Return-path: In-Reply-To: <1477673892-28940-2-git-send-email-tj@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org Hi Tejun, > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 94732d1..f6baa38 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3336,11 +3336,17 @@ static void __sched notrace __schedule(bool preempt) > unsigned long *switch_count; > struct pin_cookie cookie; > struct rq *rq; > - int cpu; > + int cpu, in_iowait; > > cpu = smp_processor_id(); > rq = cpu_rq(cpu); > prev = rq->curr; > + in_iowait = prev->in_iowait; > + > + if (in_iowait) { > + delayacct_blkio_start(); > + atomic_inc(&rq->nr_iowait); > + } > > schedule_debug(prev); > > @@ -3406,6 +3412,11 @@ static void __sched notrace __schedule(bool preempt) > } > > balance_callback(rq); > + > + if (in_iowait) { > + atomic_dec(&rq->nr_iowait); > + delayacct_blkio_end(); > + } > } I think, the nr_iowait update can go wrong here. When the task migrates to a different CPU upon wakeup, this rq points to a different CPU from the one on which nr_iowait is incremented before. Thanks, Pavan -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project