From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EB60CC4361B for ; Mon, 7 Dec 2020 16:07:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B61B323741 for ; Mon, 7 Dec 2020 16:07:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727444AbgLGQHa (ORCPT ); Mon, 7 Dec 2020 11:07:30 -0500 Received: from mail.kernel.org ([198.145.29.99]:52332 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725994AbgLGQHa (ORCPT ); Mon, 7 Dec 2020 11:07:30 -0500 Date: Mon, 7 Dec 2020 08:06:48 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1607357209; bh=i+seZr7VqfNGgwLm3kHrQbZ8rgv9VLIp3uYfQdQVJtQ=; h=From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=cL8X5GJdOEVM+H9bXQR9RCtpf+86SWG4qOBw197I6JTlLQDbl5nEI5gZgtW0uKIdp VUYyCInp5joOPrwaaaLxfUy8VKYvwfMN7lzw8c2NbGtNMiEJuvPcFD+/YVgHcQwBdt VwLJPKNrqYsJ/Qid1fKSeidZoudUPvWxZptq6prT9dJe/GJCTaWps2VANIVi+w85Qk SS+M80+UaYn+AUuEOL+2E+XWrTUhv31OVh0dYyKWif+iIX5QQmi4zsuTrdlnFvS49J qBhhWIoK//R3Cm/s9jl7fu1uAjn3qGFXdFd5hLMwyvJ8Py/TMMjNVil+YminFZJMqF w+FyHxU+3X5yw== From: "Paul E. McKenney" To: Sebastian Andrzej Siewior Cc: Thomas Gleixner , LKML , Marco Elver , kasan-dev , Peter Zijlstra , Anna-Maria Behnsen Subject: Re: timers: Move clearing of base::timer_running under base::lock Message-ID: <20201207160648.GF2657@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <87lfea7gw8.fsf@nanos.tec.linutronix.de> <20201207130753.kpxf2ydroccjzrge@linutronix.de> <87a6up7kpt.fsf@nanos.tec.linutronix.de> <20201207152533.rybefuzd57kxxv57@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201207152533.rybefuzd57kxxv57@linutronix.de> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 07, 2020 at 04:25:33PM +0100, Sebastian Andrzej Siewior wrote: > On 2020-12-07 15:29:50 [+0100], Thomas Gleixner wrote: > > On Mon, Dec 07 2020 at 14:07, Sebastian Andrzej Siewior wrote: > > > One thing I noticed while testing it is that the "corner" case in > > > timer_sync_wait_running() is quite reliably hit by rcu_preempt > > > rcu_gp_fqs_loop() -> swait_event_idle_timeout_exclusive() invocation. > > > > I assume it's something like this: > > > > timeout -> wakeup > > > > ->preemption > > del_timer_sync() > > ..... > > Yes, but it triggers frequently. Like `rcuc' is somehow is aligned with > the timeout. Given that a lot of RCU processing is event-driven based on timers, and given that the scheduling-clock interrupts are synchronized for energy-efficiency reasons on many configs, maybe this alignment is expected behavior? Thanx, Paul > | -0 [007] dN.h4.. 46.299705: sched_wakeup: comm=rcuc/7 pid=53 prio=98 target_cpu=007 > | -0 [007] d...2.. 46.299728: sched_switch: prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=rcuc/7 next_pid=53 next_prio=98 > | rcuc/7-53 [007] d...2.. 46.299742: sched_switch: prev_comm=rcuc/7 prev_pid=53 prev_prio=98 prev_state=S ==> next_comm=ksoftirqd/7 next_pid=54 next_prio=120 > | ksoftirqd/7-54 [007] .....13 46.299750: timer_expire_entry: timer=000000003bd1e045 function=process_timeout now=4294903802 baseclk=4294903802 > | ksoftirqd/7-54 [007] d...213 46.299750: sched_waking: comm=rcu_preempt pid=11 prio=98 target_cpu=007 > | ksoftirqd/7-54 [007] dN..313 46.299754: sched_wakeup: comm=rcu_preempt pid=11 prio=98 target_cpu=007 > | ksoftirqd/7-54 [007] dN..213 46.299756: sched_stat_runtime: comm=ksoftirqd/7 pid=54 runtime=13265 [ns] vruntime=3012610540 [ns] > | ksoftirqd/7-54 [007] d...213 46.299760: sched_switch: prev_comm=ksoftirqd/7 prev_pid=54 prev_prio=120 prev_state=R+ ==> next_comm=rcu_preempt next_pid=11 next_prio=98 > | rcu_preempt-11 [007] d...311 46.299766: sched_pi_setprio: comm=ksoftirqd/7 pid=54 oldprio=120 newprio=98 > del_timer_sync() > | rcu_preempt-11 [007] d...211 46.299773: sched_switch: prev_comm=rcu_preempt prev_pid=11 prev_prio=98 prev_state=R+ ==> next_comm=ksoftirqd/7 next_pid=54 next_prio=98 > | ksoftirqd/7-54 [007] .....13 46.299774: timer_expire_exit: timer=000000003bd1e045 > | ksoftirqd/7-54 [007] dN..311 46.299784: sched_pi_setprio: comm=ksoftirqd/7 pid=54 oldprio=98 newprio=120 > | ksoftirqd/7-54 [007] dN..311 46.299788: sched_waking: comm=rcu_preempt pid=11 prio=98 target_cpu=007 > | ksoftirqd/7-54 [007] dN..411 46.299790: sched_wakeup: comm=rcu_preempt pid=11 prio=98 target_cpu=007 > | ksoftirqd/7-54 [007] dN..311 46.299792: sched_stat_runtime: comm=ksoftirqd/7 pid=54 runtime=7404 [ns] vruntime=3012617944 [ns] > | ksoftirqd/7-54 [007] d...2.. 46.299797: sched_switch: prev_comm=ksoftirqd/7 prev_pid=54 prev_prio=120 prev_state=S ==> next_comm=rcu_preempt next_pid=11 next_prio=98 > > > > Thanks, > > > > tglx > > Sebastian