Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753264AbbLSFym (ORCPT ); Sat, 19 Dec 2015 00:54:42 -0500 Received: from mail-pa0-f52.google.com ([209.85.220.52]:34398 "EHLO mail-pa0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752196AbbLSFyk (ORCPT ); Sat, 19 Dec 2015 00:54:40 -0500 Date: Sat, 19 Dec 2015 13:54:32 +0800 From: Leo Yan To: Steve Muckle Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Vincent Guittot , Morten Rasmussen , Dietmar Eggemann , Juri Lelli , Patrick Bellasi , Michael Turquette , Ricky Liang Subject: Re: [RFCv6 PATCH 03/10] sched: scheduler-driven cpu frequency selection Message-ID: <20151219055432.GB23305@leoy-linaro> References: <1449641971-20827-1-git-send-email-smuckle@linaro.org> <1449641971-20827-4-git-send-email-smuckle@linaro.org> <20151216034825.GA11303@leoy-linaro> <56720EE8.1090507@linaro.org> <20151217071733.GB6195@leoy-linaro> <56745B35.5050704@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56745B35.5050704@linaro.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2597 Lines: 70 Hi Steve, On Fri, Dec 18, 2015 at 11:15:01AM -0800, Steve Muckle wrote: > On 12/16/2015 11:17 PM, Leo Yan wrote: > > Could you check if below corner case will introduce logic error? > > The task still will be removed from rq if timer tick is triggered > > between two time's set_current_state(). > > > > set_current_state(TASK_INTERRUPTIBLE); > > `-------> timer_tick and > > schedule(); > > do_something... > > set_current_state(TASK_RUNNING); > > > > It will be safe for combination for set_current_state()/schedule() > > with waken_up_process(): > > > > Thread_A: Thread_B: > > > > set_current_state(TASK_INTERRUPTIBLE); > > `-------> timer_tick and > > schedule(); > > .... > > wake_up_process(Thread_A); > > <---------------------/ > > schedule(); > > > > The first time's schedule() will remove task from rq which is caused > > by timer tick and call schedule(), and the second time schdule() will > > be equal yeild(). > > I was initially concerned about preemption while task state = > TASK_INTERRUPTIBLE as well, but a task with state TASK_INTERRUPTIBLE is > not dequeued if it is preempted. See core.c:__schedule(): > > if (!preempt && prev->state) { > if (unlikely(signal_pending_state(prev->state, prev))) { > prev->state = TASK_RUNNING; > } else { > deactivate_task(rq, prev, DEQUEUE_SLEEP); > prev->on_rq = 0; > > I knew this had to be the case, because this design pattern is used in > many other places in the kernel, so many things would be very broken if > this were a problem. You are right, I went through the code again and sched tick irq will call preempt_schedule_irq() and __schedule(true); so finally set the parameter "preempt" = true. Sorry for noise :p ---8<--- arch/arm64/kernel/entry.S: #ifdef CONFIG_PREEMPT el1_preempt: mov x24, lr 1: bl preempt_schedule_irq // irq en/disable is done inside ldr x0, [tsk, #TI_FLAGS] // get new tasks TI_FLAGS tbnz x0, #TIF_NEED_RESCHED, 1b // needs rescheduling? ret x24 #endif Thanks, Leo Yan -- 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/