Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932809AbbKROEC (ORCPT ); Wed, 18 Nov 2015 09:04:02 -0500 Received: from foss.arm.com ([217.140.101.70]:34889 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932719AbbKROD7 (ORCPT ); Wed, 18 Nov 2015 09:03:59 -0500 Date: Wed, 18 Nov 2015 14:04:41 +0000 From: Morten Rasmussen To: Peter Zijlstra Cc: Ingo Molnar , Jacob Pan , Ingo Molnar , Thomas Gleixner , John Stultz , LKML , Arjan van de Ven , Srinivas Pandruvada , Len Brown , Rafael Wysocki , Eduardo Valentin , Paul Turner Subject: Re: [PATCH 3/4] sched: introduce synchronized idle injection Message-ID: <20151118140440.GB30184@e105550-lin.cambridge.arm.com> References: <1447444387-23525-1-git-send-email-jacob.jun.pan@linux.intel.com> <1447444387-23525-4-git-send-email-jacob.jun.pan@linux.intel.com> <20151118083622.GA25217@gmail.com> <20151118103541.GE3816@twins.programming.kicks-ass.net> <20151118122702.GA30184@e105550-lin.cambridge.arm.com> <20151118124946.GF3816@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151118124946.GF3816@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 Content-Length: 1803 Lines: 44 On Wed, Nov 18, 2015 at 01:49:46PM +0100, Peter Zijlstra wrote: > On Wed, Nov 18, 2015 at 12:27:04PM +0000, Morten Rasmussen wrote: > > On Wed, Nov 18, 2015 at 11:35:41AM +0100, Peter Zijlstra wrote: > > > On Wed, Nov 18, 2015 at 09:36:22AM +0100, Ingo Molnar wrote: > > > > What will such throttling do to latencies, as observed by user-space tasks? What's > > > > the typical expected frequency of the throttling frequency that you are targeting? > > > > > > The default has 5ms (iirc) of forced idle, so depending on what you do, > > > noticeable to outright painful. > > > > IIUC, it is 5 ticks, not ms. > > The code uses hrtimers (badly), this means there _should_ not be a tick > dependency. Then I'm confused :-/ I see the hrtimers, but the actual idle duration appears to be in ticks rather than ms and then converted later. +/* Duration of idle time in ticks of each injection period */ +unsigned int sysctl_sched_cfs_idle_inject_duration = 5UL; ...and futher down we have: + duration_msec = jiffies_to_msecs(sysctl_sched_cfs_idle_inject_duration); I will go back and look harder. > > > Which raises the question, doesn't that mean that we get disturbed four > > times on each cpu during the forced idle period? So idle injection only > > makes sense if the platform has package states with a target residency > > less than a jiffy. Or, do we enter NOHZ idle? I haven't looked closely > > enough to figure out yet. > > The idea is to hit NOHZ. Nice! -- 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/