From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754975AbaDNMGL (ORCPT ); Mon, 14 Apr 2014 08:06:11 -0400 Received: from merlin.infradead.org ([205.233.59.134]:50788 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754945AbaDNMGH (ORCPT ); Mon, 14 Apr 2014 08:06:07 -0400 Date: Mon, 14 Apr 2014 14:06:00 +0200 From: Peter Zijlstra To: Viresh Kumar Cc: Frederic Weisbecker , 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: <20140414120600.GJ11096@twins.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 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. 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.