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=-7.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 428C3C4363A for ; Mon, 26 Oct 2020 14:42:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F15FD22281 for ; Mon, 26 Oct 2020 14:42:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603723378; bh=bpuObpcLJtZiDmzQS2y2dFX1l3G60DHiaBNVEThZDbU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=EmDYzFhzDNYp6G8qoRysS8aiCbu/JiiZ8L9tcZLMp7yWw4FBbHIObMc/IKg14ajlj kGA5YyNyh54tMZbDDHIBvegmdwqmqkqy/prB3x9Au0mQKAo8xuXAazp3nJa37QYmu6 y42imjKG0WDL4cJfP0LgE92As7F0LaYtUYgqkeTE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1781843AbgJZOm4 (ORCPT ); Mon, 26 Oct 2020 10:42:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:35306 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1781724AbgJZOm4 (ORCPT ); Mon, 26 Oct 2020 10:42:56 -0400 Received: from localhost (bny93-h09-176-172-152-46.dsl.sta.abo.bbox.fr [176.172.152.46]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6767722263; Mon, 26 Oct 2020 14:42:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603723375; bh=bpuObpcLJtZiDmzQS2y2dFX1l3G60DHiaBNVEThZDbU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fUVz3TRnfuRrFaO/UAEVAr9jUymYgKp/NAytBrlIhlN2CgjYE1yYNJDMS2PImwoM3 IzmWevNpz4hxj6Myk55TEOpz+54cPW7VNOSLUXGigLvHuV1h9QepGVyMcUmyTezrHU 4ntZU9tWMjK5NRxRAfeGiiFSJr9ExqCxM277aYo4= Date: Mon, 26 Oct 2020 15:42:53 +0100 From: Frederic Weisbecker To: Peter Zijlstra Cc: Marcelo Tosatti , linux-kernel@vger.kernel.org, Nitesh Narayan Lal , Peter Xu Subject: Re: [patch 1/2] nohz: only wakeup a single target cpu when kicking a task Message-ID: <20201026144253.GB120760@lothringen> References: <20201007180151.623061463@redhat.com> <20201007180229.724302019@redhat.com> <20201008122256.GW2628@hirez.programming.kicks-ass.net> <20201008175409.GB14207@fuller.cnet> <20201008195444.GB86389@lothringen> <20201013171328.GA19284@fuller.cnet> <20201014083321.GA2628@hirez.programming.kicks-ass.net> <20201014234053.GA86158@lothringen> <20201015101235.GA2611@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201015101235.GA2611@hirez.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 15, 2020 at 12:12:35PM +0200, Peter Zijlstra wrote: > On Thu, Oct 15, 2020 at 01:40:53AM +0200, Frederic Weisbecker wrote: > > > re tick_nohz_task_switch() being placed wrong, it should probably be > > > placed before finish_lock_switch(). Something like so. > > > > > > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > > index cf044580683c..5c92c959824f 100644 > > > --- a/kernel/sched/core.c > > > +++ b/kernel/sched/core.c > > > @@ -4084,6 +4084,7 @@ static struct rq *finish_task_switch(struct task_struct *prev) > > > vtime_task_switch(prev); > > > perf_event_task_sched_in(prev, current); > > > finish_task(prev); > > > + tick_nohz_task_switch(); > > > finish_lock_switch(rq); > > > finish_arch_post_lock_switch(); > > > kcov_finish_switch(current); > > > @@ -4121,7 +4122,6 @@ static struct rq *finish_task_switch(struct task_struct *prev) > > > put_task_struct_rcu_user(prev); > > > } > > > > > > - tick_nohz_task_switch(); > > > > IIRC, we wanted to keep it outside rq lock because it shouldn't it... > > But now you've created a window with IRQs on and cause additional IRQ > state changes. > > If you're really worried about rq->lock, I suppose we can do: > > rq_unlock(rq->lock); > tick_nohz_task_switch(); > local_irq_enable(); > > (much like we do at the beginning of __schedule for RCU) Right. Well I'm not that worried about rq->lock though. If you're ok with it I can just move it before finish_lock_switch(). Thanks.