Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755743AbaGZTl1 (ORCPT ); Sat, 26 Jul 2014 15:41:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39502 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753036AbaGZTlY (ORCPT ); Sat, 26 Jul 2014 15:41:24 -0400 Date: Sat, 26 Jul 2014 21:39:10 +0200 From: Oleg Nesterov To: Kirill Tkhai Cc: linux-kernel@vger.kernel.org, nicolas.pitre@linaro.org, peterz@infradead.org, pjt@google.com, rostedt@goodmis.org, umgwanakikbuti@gmail.com, ktkhai@parallels.com, tim.c.chen@linux.intel.com, mingo@kernel.org Subject: Re: [PATCH v2 0/5] sched: Add on_rq states and remove several double rq locks Message-ID: <20140726193910.GA8420@redhat.com> References: <20140726145508.6308.69121.stgit@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140726145508.6308.69121.stgit@localhost> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Kirill, I'll try to read this series later, just one silly question for now. On 07/26, Kirill Tkhai wrote: > > Patch [2/5] is main in the series. It introduces new state: ONRQ_MIGRATING > and teaches scheduler to understand it (we need a little changes predominantly > in try_to_wake_up()). This will be used in the following way: > > (we are changing task's rq) > > raw_spin_lock(&src_rq->lock); > dequeue_task(src_rq, p, 0); > p->on_rq = ONRQ_MIGRATING; > set_task_cpu(p, dst_cpu); > raw_spin_unlock(&src_rq->lock); > > raw_spin_lock(&dst_rq->lock); > p->on_rq = ONRQ_QUEUED; > enqueue_task(dst_rq, p, 0); > raw_spin_unlock(&dst_rq->lock); Hmm. And what if the code above doesn't hold p->pi_lock (4/5) and, say, __sched_setscheduler() does fair_sched_class->rt_sched_class transition in between? ONRQ_MIGRATING helps to avoid the wrong dequeue + enqueue, but I am not sure about check_class_changed(). Say, switched_from_fair() will use dst_rq even if p was never queued on this rq... This only affects the .decay_count logic, perhaps this is fine, I simply do not know what this code does. What about switched_to_rt() ? we lose the push_rt_task() logic... Hmm, which I can't understand too ;) And we also lose ENQUEUE_HEAD in this case, but this looks fine. In short: could you confirm there are no problems here? Oleg. -- 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/