From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752796AbcFQUgX (ORCPT ); Fri, 17 Jun 2016 16:36:23 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:34604 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750725AbcFQUgV (ORCPT ); Fri, 17 Jun 2016 16:36:21 -0400 Date: Fri, 17 Jun 2016 22:36:12 +0200 From: luca abeni To: Juri Lelli Cc: Steven Rostedt , linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@redhat.com Subject: Re: [PATCH] sched/deadline: remove useless param from setup_new_dl_entity Message-ID: <20160617223612.2c8bf505@utopia> In-Reply-To: <20160617221518.75427592@utopia> References: <1466156921-12417-1-git-send-email-juri.lelli@arm.com> <20160617094935.1d4df586@gandalf.local.home> <20160617162837.GQ5981@e106622-lin> <20160617221518.75427592@utopia> X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; i686-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 17 Jun 2016 22:15:18 +0200 luca abeni wrote: > On Fri, 17 Jun 2016 17:28:37 +0100 > Juri Lelli wrote: > [...] > > True, but we were practically already using the same parameter, under a > > different name though, after > > > > 2f9f3fdc928 "sched/deadline: Remove dl_new from struct sched_dl_entity" > > > > as we currently do: > > > > setup_new_dl_entity(&p->dl, &p->dl) > > > > > This patch reverts part of the change done in > > > commit 2d3d891d334 "sched/deadline: Add SCHED_DEADLINE inheritance > > > logic" > > > > > > > Before Luca's change we were doing > > > > setup_new_dl_entity(dl_se, pi_se) > > > > in update_dl_entity() for a dl_se->new entity. So, I guess the question > > is actually why we wanted to use pi_se's parameters (the potential PI > > donor) for setting up a new entity? > That's a good question :) > > > Maybe we broke the situation where a > > task is currently boosted by a DEADLINE waiter and we swich the holder > > to DEADLINE? > I remember I tested this setup (using linaro's version of rt-app), and > it seemed to work correctly... > > Re-reading the code now, I actually wonder why my patch did not break > inheritance in this situation... Ok; I think I know why inheritance is not broken (or, at least, it does not appear to be broken when testing it with rt-app): - When a -deadline task blocks on a mutex that is held by a SCHED_OTHER or SCHED_FIFO task, such a task is promoted to -deadline - setup_new_dl_entity() is invoked, and it sets the tasks' deadline to rq_clock(rq) (+ 0), so the task holding the lock is immediately scheduled - as soon as update_curr_dl() is invoked (in the worst case at the next tick), the task's deadline and runtime are set to the "desired values" (using pi_se) So, the behaviour is not changed too much respect to the previous one. Luca