Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1168942AbdDXKxE (ORCPT ); Mon, 24 Apr 2017 06:53:04 -0400 Received: from foss.arm.com ([217.140.101.70]:55342 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1168642AbdDXKxA (ORCPT ); Mon, 24 Apr 2017 06:53:00 -0400 Date: Mon, 24 Apr 2017 11:53:13 +0100 From: Juri Lelli To: Luca Abeni Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Ingo Molnar , Claudio Scordino , Steven Rostedt , Tommaso Cucinotta , Daniel Bristot de Oliveira , Mathieu Poirier Subject: Re: [PATCH] sched/deadline: fix switching to -deadline Message-ID: <20170424105313.GB13394@e106622-lin> References: <1492716656-5362-1-git-send-email-luca.abeni@santannapisa.it> <20170421093926.GQ23862@e106622-lin> <20170421114240.0ef43522@nowhere> <20170421094729.GR23862@e106622-lin> <20170421115907.4044665a@nowhere> <20170421102659.GS23862@e106622-lin> <20170421210833.1837de6f@sweethome> <20170424101624.GA13394@e106622-lin> <20170424123615.1d2033c9@luca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170424123615.1d2033c9@luca> 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: 2990 Lines: 69 On 24/04/17 12:36, Luca Abeni wrote: > On Mon, 24 Apr 2017 11:16:24 +0100 > Juri Lelli wrote: > > > On 21/04/17 21:08, Luca Abeni wrote: [...] > > > > > > Well, double thinking about it, this is an interesting problem... > > > What do we want to do with do_set_cpus_allowed()? (I mean: what is > > > the expected behaviour?) > > > > > > With this patch, if a task is moved to a different runqueue when its > > > deadline is in the past (because we are doing gEDF, or because of > > > timer granularity issues) its scheduling deadline is reinitialized > > > to current time + relative deadline... I think this makes perfect > > > sense, doesn't it? > > > > > > > Mmm, I don't think we will (with this patch) actually reinitialize the > > deadline when a "normal" gEDF migration happen (push/pull), as > > (de)activate_task() have no flag set. Which brings the question, > > should we actually take care of this corner case (as what you say > > makes sense to me too)? > > I might be misunderstanding the problem, here... Are you talking about > do_set_cpus_allowed()? Or about push/pull migrations happening because > of the gEDF algorithm? > My concern was about do_set_cpus_allowed(), but then you mentioned "because we are doing gEDF" and that made me think of what happens when we do push/pull. :) > If you are referring to do_set_cpus_allowed, this is my understanding: > 1) If do_set_cpus_allowed() is called on a queued task, then > dequeue_task() with DEQUEUE_SAVE is called, followed by > enqueue_task() with ENQUEUE_RESTORE... So, if the deadline is in the > past it is correctly reinitialized > 2) If do_set_cpus_allowed() is called on a non-queued task, this means > the task is blocked, no? So, when it will wake up enqueue_dl_entity() > will invoke update_dl_entity() that will check if the deadline is in > the past. > OK. I think it makes sense, and your patch should cure the problem. Maybe add a comment to note this down. > If you are referring to push/pull migrations due to gEDF, then > enqueue_dl_entity() will be invoked with "flags" = 0, so the deadline > will not be changed (and this is correct: we do not want to > initialize / change tasks' deadlines during gEDF migrations). > Ok, but I was wondering about the (admittedly) corner case in which we migrate (via push/pull) a task on a rq, the rq_clock of which is after the task's deadline (because clocks on src_rq and dst_rq are not in sync). Anyway, maybe it's so corner case that we don't really want to deal with it right now? I guess bigger things to fix first. :) > In my previous email, with "a task is moved to a different runqueue" I > wanted to say that the taks is forced to moved to a different runqueue > because its affinity is changed; I did not want to talk about "regular > migrations" due to the push/pull (gEDF) mechanism. > Thanks for claryfing. As said, I just got distracted by what you mentioned as examples between parenthesis.