Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755143AbaDNLrw (ORCPT ); Mon, 14 Apr 2014 07:47:52 -0400 Received: from merlin.infradead.org ([205.233.59.134]:50691 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754511AbaDNLru (ORCPT ); Mon, 14 Apr 2014 07:47:50 -0400 Date: Mon, 14 Apr 2014 13:47:44 +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: <20140414114744.GI11096@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> 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 05:12:08PM +0530, Viresh Kumar wrote: > On 14 April 2014 16:32, Peter Zijlstra wrote: > > I'm still not sure _what_ you're trying to solve here. What are you > > doing and why? > > Hi Peter, > > We are working building ARM Networking machines. Networking Data > plane is handled completely at user space. At run time we may fix > any number of CPUs for data plane activities. There will be a single > user space thread per CPU for these data plane packet processing. > Due to timing constraints these cores can't allow any interruption > from kernel. These include interruption from: > > - other tasks: Fixed with cpusets > - timers/hrtimers: Implemented cpuset.quiesce as you suggested: > Waiting for reviews > - workqueues: Probably would be fixed by Frederic's work. Ok. > - Tick: Even with NO_HZ_FULL we get a tick every second. This is > what I am trying to address here. Frederic earlier suggested to > offload this accounting to other CPUs and so was my initial proposal. 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. -- 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/