From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751074AbcBJMtG (ORCPT ); Wed, 10 Feb 2016 07:49:06 -0500 Received: from mail-wm0-f68.google.com ([74.125.82.68]:34834 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750825AbcBJMtE (ORCPT ); Wed, 10 Feb 2016 07:49:04 -0500 Date: Wed, 10 Feb 2016 13:48:48 +0100 From: luca abeni To: Juri Lelli Cc: rostedt@goodmis.org, linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org, wanpeng.li@hotmail.com Subject: Re: [PATCH 1/2] sched/deadline: add per rq tracking of admitted bandwidth Message-ID: <20160210134848.12e6a6f8@utopia> In-Reply-To: <20160210113258.GX11415@e106622-lin> References: <1454935531-7541-1-git-send-email-juri.lelli@arm.com> <1454935531-7541-2-git-send-email-juri.lelli@arm.com> <20160210113258.GX11415@e106622-lin> Organization: university of trento X-Mailer: Claws Mail 3.12.0 (GTK+ 2.24.28; x86_64-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 Hi, On Wed, 10 Feb 2016 11:32:58 +0000 Juri Lelli wrote: [...] > From 62f70ca3051672dce209e8355cf5eddc9d825c2a Mon Sep 17 00:00:00 2001 > From: Juri Lelli > Date: Sat, 6 Feb 2016 12:41:09 +0000 > Subject: [PATCH 1/2] sched/deadline: add per rq tracking of admitted > bandwidth > > Currently SCHED_DEADLINE scheduling policy tracks bandwidth of tasks > that passed admission control at root_domain level only. This creates > problems when such data structure(s) are destroyed, when we > reconfigure scheduling domains for example. > > This is part one of two changes required to fix the problem. In this > patch we add per-rq tracking of admitted bandwidth. Tasks bring with > them their bandwidth contribution when they enter the system and are > enqueued for the first time. Contributions are then moved around when > migrations happen and removed when tasks die. I think this patch actually does two different things (addressing two separate problems): 1) it introduces the tracking of per-rq utilization (used in your next patch to address the root domain issues) 2) it fixes a bug in the current utilization tracking mechanism. Currently, a task doing while(1) { switch to SCHED_DEADLINE switch to SCHED_OTHER } brings dl_b->total_bw below 0. Thanks to Juri for showing me this problem (and how to reproduce it) in a private email. This happens because when the task switches back from SCHED_DEADLINE to SCHED_OTHER, switched_from_dl() does not clear its deadline parameters (they will be cleared by the deadline timer when it fires). But dl_overflow() removes its utilization from dl_b->total_bw. When the task switches back to SCHED_DEADLINE, the if (new_bw == p->dl.dl_bw) check in dl_overflow() prevents __dl_add() from being called, and so when the task switches back to SCHED_OTHER dl_b->total_bw becomes negative. > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 9503d59..0ee0ec2 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2432,7 +2432,7 @@ static int dl_overflow(struct task_struct *p, > int policy, u64 new_bw = dl_policy(policy) ? to_ratio(period, > runtime) : 0; int cpus, err = -1; > > - if (new_bw == p->dl.dl_bw) > + if (task_has_dl_policy(p) && new_bw == p->dl.dl_bw) > return 0; This hunk actually fixes issue 2) mentioned above, so I think it should be committed in a short time (independently from the rest of the patch). And maybe is a good candidate for backporting to stable kernels? Thanks, Luca