Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754033AbaDOJaM (ORCPT ); Tue, 15 Apr 2014 05:30:12 -0400 Received: from mail-wi0-f175.google.com ([209.85.212.175]:35335 "EHLO mail-wi0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751671AbaDOJaH (ORCPT ); Tue, 15 Apr 2014 05:30:07 -0400 Date: Tue, 15 Apr 2014 11:30:04 +0200 From: Frederic Weisbecker To: Peter Zijlstra Cc: Viresh Kumar , Thomas Gleixner , Linux Kernel Mailing List , Lists linaro-kernel Subject: Re: [Query]: tick-sched: why don't we stop tick when we are running idle task? Message-ID: <20140415093002.GL1877@localhost.localdomain> References: <20140410143857.GA27654@localhost.localdomain> <20140411145333.GC3438@localhost.localdomain> <20140411151825.GX11096@twins.programming.kicks-ass.net> <20140414110245.GG11096@twins.programming.kicks-ass.net> <20140414114744.GI11096@twins.programming.kicks-ass.net> <20140414120600.GJ11096@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140414120600.GJ11096@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 14, 2014 at 02:06:00PM +0200, Peter Zijlstra wrote: > On Mon, Apr 14, 2014 at 05:22:30PM +0530, Viresh Kumar wrote: > > On 14 April 2014 17:17, Peter Zijlstra wrote: > > > What causes this tick? I was under the impression that once there's a > > > single task (not doing any syscalls) and the above issues are sorted, no > > > more tick would happen. > > > > This is what Frederic told me earlier: > > > > https://lkml.org/lkml/2014/2/13/238 > > That's a bit of a non-answer. I'm fairly sure its not a gazillion > issues, since the actual scheduler tick doesn't actually do that much. > > So start by enumerating what is actually required. Ok, I'm a bit buzy with a conference right now but I'm going to summarize that soonish. > > The 2), which I suppose you're now trying to implement is I think > entirely the wrong way. The tick really assumes it runs local, moving it > to another CPU is insane. There is probably a few things that assume local calls but last time I checked I had the impression that it was fairly possible to call sched_class::task_tick() remotely. rq is locked, no reference to "current", use rq accessors... OTOH scheduler_tick() itself definetly requires local calls. -- 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/