From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752281Ab2GIGvS (ORCPT ); Mon, 9 Jul 2012 02:51:18 -0400 Received: from merlin.infradead.org ([205.233.59.134]:42730 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752082Ab2GIGvB convert rfc822-to-8bit (ORCPT ); Mon, 9 Jul 2012 02:51:01 -0400 Message-ID: <1341816515.3462.3.camel@twins> Subject: Re: [Question] sched/rt_mutex: re-enqueue_task on rt_mutex_setprio() From: Peter Zijlstra To: Namhyung Kim Cc: Steven Rostedt , Ingo Molnar , LKML Date: Mon, 09 Jul 2012 08:48:35 +0200 In-Reply-To: <87obnp92r8.fsf@sejong.aot.lge.com> References: <87zk7cgm6u.fsf@sejong.aot.lge.com> <1341710959.2783.2.camel@acer.local.home> <87obnp92r8.fsf@sejong.aot.lge.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2012-07-09 at 09:50 +0900, Namhyung Kim wrote: > On Sat, 07 Jul 2012 21:29:19 -0400, Steven Rostedt wrote: > > On Sat, 2012-07-07 at 14:44 +0900, Namhyung Kim wrote: > >> Hi, > >> > >> I have a question on the code below: > >> > >> void rt_mutex_setprio(struct task_struct *p, int prio) > >> { > >> ... > >> if (on_rq) > >> enqueue_task(rq, p, oldprio < prio ? ENQUEUE_HEAD : 0); > >> > >> When enqueueing @p with new @prio, it seems put @p at the head of a > >> rq if appropriate. I guess it's the case of boosting @p with higher > >> priority, right? > > > > Actually, no. We put @p at the head of the queue when unboosting. If a > > task is going from a high priority into a lower priority, it is still > > treated as "important" for that priority, and is put to the front of the > > queue (it was just higher than everything else on that queue). But if we > > are boosting a task from a low priority, why put it to the head of other > > tasks of its new priority, when those tasks were just higher than this > > task, and this task is now just an "equal". > > Thanks for the explanation. (Isn't it worth getting commented?) :) Possibly, note that this part is well spec'ed by POSIX, see http://pubs.opengroup.org/onlinepubs/009695299/functions/xsh_chap02_08.html SCHED_FIFO.8