From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752085Ab0CYQE5 (ORCPT ); Thu, 25 Mar 2010 12:04:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55237 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751282Ab0CYQEz (ORCPT ); Thu, 25 Mar 2010 12:04:55 -0400 Date: Thu, 25 Mar 2010 17:02:43 +0100 From: Oleg Nesterov To: Peter Zijlstra Cc: Ingo Molnar , Ben Blum , Jiri Slaby , Lai Jiangshan , Li Zefan , Miao Xie , Paul Menage , "Rafael J. Wysocki" , Tejun Heo , linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/6] sched/cpusets fixes, more changes are needed Message-ID: <20100325160243.GA11517@redhat.com> References: <20100315090958.GA9116@redhat.com> <1269452296.5109.508.camel@twins> <20100324180912.GA21774@redhat.com> <1269512531.12097.67.camel@laptop> <20100325154616.GA9773@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100325154616.GA9773@redhat.com> 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 On 03/25, Oleg Nesterov wrote: > > I like the current idea to call select_task_rq() without rq->lock, but > of course this is up to you. > > However, once again, can't we make a simpler patch? > > - remove PF_STARTING from task_waking() > > - change sched_fork() to set RUNNING instead of WAKING > > - change wake_up_new_task() to set WAKING under rq->lock > > This looks simpler to me, and allows to drop rq->lock in ttwu() right > after it sets WAKING. IOW, something like the (unchecked, uncompiled) patch below. What do you think? Oleg. --- x/kernel/sched.c +++ x/kernel/sched.c @@ -912,7 +912,7 @@ static inline void finish_lock_switch(st */ static inline int task_is_waking(struct task_struct *p) { - return unlikely((p->state == TASK_WAKING) && !(p->flags & PF_STARTING)); + return unlikely(p->state == TASK_WAKING); } /* @@ -2568,11 +2568,10 @@ void sched_fork(struct task_struct *p, i __sched_fork(p); /* - * We mark the process as waking here. This guarantees that - * nobody will actually run it, and a signal or other external - * event cannot wake it up and insert it on the runqueue either. + * We mark the process as running here. This guarantees that + * nobody will actually wake it up until wake_up_new_task(). */ - p->state = TASK_WAKING; + p->state = TASK_RUNNING; /* * Revert to default priority/policy on fork if requested. @@ -2638,15 +2637,18 @@ void wake_up_new_task(struct task_struct struct rq *rq; int cpu = get_cpu(); + p->state = TASK_WAKING; + smp_mb(); + raw_spin_unlock_wait(&rq->lock); + #ifdef CONFIG_SMP /* * Fork balancing, do it here and not earlier because: * - cpus_allowed can change in the fork path * - any previously selected cpu might disappear through hotplug * - * We still have TASK_WAKING but PF_STARTING is gone now, meaning - * ->cpus_allowed is stable, we have preemption disabled, meaning - * cpu_online_mask is stable. + * TASK_WAKING means ->cpus_allowed is stable, we have preemption + * disabled, meaning cpu_online_mask is stable. */ cpu = select_task_rq(p, SD_BALANCE_FORK, 0); set_task_cpu(p, cpu);