Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753323Ab3JAP4r (ORCPT ); Tue, 1 Oct 2013 11:56:47 -0400 Received: from merlin.infradead.org ([205.233.59.134]:53217 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752010Ab3JAP4p (ORCPT ); Tue, 1 Oct 2013 11:56:45 -0400 Date: Tue, 1 Oct 2013 17:56:33 +0200 From: Peter Zijlstra To: Frederic Weisbecker Cc: Oleg Nesterov , Arjan van de Ven , Fernando Luis =?iso-8859-1?Q?V=E1zquez?= Cao , Ingo Molnar , Thomas Gleixner , LKML , Tetsuo Handa , Andrew Morton Subject: Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock Message-ID: <20131001155633.GR3657@laptop.programming.kicks-ass.net> References: <20130820160146.GG3258@twins.programming.kicks-ass.net> <20130820163312.GA17957@redhat.com> <20130820175429.GI3258@twins.programming.kicks-ass.net> <20130820182553.GB22287@redhat.com> <20130821083130.GM3258@twins.programming.kicks-ass.net> <20130821113551.GA1472@redhat.com> <20130821123311.GA31370@twins.programming.kicks-ass.net> <20130821142356.GC31370@twins.programming.kicks-ass.net> <20130821164146.GA15194@redhat.com> <20131001140525.GE24825@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131001140525.GE24825@localhost.localdomain> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1095 Lines: 41 So what's wrong with something like: struct cpu_idletime { seqlock_t seqlock; unsigned long nr_iowait; u64 start; u64 idle_time, u64 iowait_time, } __cacheline_aligned_in_smp; DEFINE_PER_CPU(struct cpu_idletime, cpu_idletime); void io_schedule(void) { struct cpu_idletime *it = __raw_get_cpu_var(cpu_idletime); write_seqlock(&it->seqlock); if (!it->nr_iowait++) it->start = local_clock(); write_sequnlock(&it->seqlock); current->in_iowait = 1; schedule(); current->in_iowait = 0; write_seqlock(&it->seqlock); if (!--it->nr_iowait) it->iowait_time += local_clock() - it->start; write_sequnlock(&it->seqlock); } Afaict you don't need the preempt disable and atomic muck at all. It will all get a little more complicated to deal with overlapping idle and iowait times, but the idea is the same. -- 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/