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=-0.6 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,T_DKIM_INVALID,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by aws-us-west-2-korg-lkml-1.web.codeaurora.org (Postfix) with ESMTP id 2082CC5CFF1 for ; Tue, 12 Jun 2018 15:58:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C91222087E for ; Tue, 12 Jun 2018 15:58:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="SExJJbxj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C91222087E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934430AbeFLP64 (ORCPT ); Tue, 12 Jun 2018 11:58:56 -0400 Received: from merlin.infradead.org ([205.233.59.134]:53152 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933363AbeFLP6y (ORCPT ); Tue, 12 Jun 2018 11:58:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=YZG4hNRXa1wRPlvCZTAJonMB9re/azLfZgiiOcOFB4E=; b=SExJJbxjrjCCgkuuGhZiJLaQH LCpQhn2PvrW3v1hZHyfPnJ4AALXRcMTRAcnDwy7jD7jB/y/3vKuhgphYAj2wZK2WljdCNxgqajZJf H1MNehou56m4aj4NUVdwVo8FXLZBz4MBh+kOumJlrVPCtZLQisC0mR7B9WyQX2yrTEYXj8tIRhJK5 VZZpALkvTb22wFOJ9xr0QhnORXzooI5Bf2T6231Qlg2QPoRBKtvpRG39xINZ2puGoMpr4BTNmD+gq tcpTlf+KfaztlyyJk1V6giqqAaiIKUzGtPDxctJhb0916B0LL/6IaGNBZK3jZZmBjo16BfwpWFpKv nO+35ueHg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fSlgy-0004cg-Q5; Tue, 12 Jun 2018 15:58:45 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id AA58A201EA7A5; Tue, 12 Jun 2018 17:58:41 +0200 (CEST) Date: Tue, 12 Jun 2018 17:58:41 +0200 From: Peter Zijlstra To: Daniel Lezcano Cc: viresh.kumar@linaro.org, rjw@rjwysocki.net, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Eduardo Valentin , Javi Merino , Leo Yan , Kevin Wangtao , Vincent Guittot , Rui Zhang , Daniel Thompson , Andrea Parri Subject: Re: [PATCH V6] powercap/drivers/idle_injection: Add an idle injection framework Message-ID: <20180612155841.GT12217@hirez.programming.kicks-ass.net> References: <1528804816-32636-1-git-send-email-daniel.lezcano@linaro.org> <20180612123036.GJ12180@hirez.programming.kicks-ass.net> <16d5649d-863c-10c7-9287-202568e713e6@linaro.org> <20180612125247.GO12217@hirez.programming.kicks-ass.net> <16770447-afe3-0fd7-19f9-1bd52c4c8ced@linaro.org> <20180612140654.GQ12217@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.5 (2018-04-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 12, 2018 at 04:37:17PM +0200, Daniel Lezcano wrote: > On 12/06/2018 16:06, Peter Zijlstra wrote: > > On Tue, Jun 12, 2018 at 03:02:14PM +0200, Daniel Lezcano wrote: > >> On 12/06/2018 14:52, Peter Zijlstra wrote: > >>> In this case, you can do: > >> > >> That is what we had before but we change the code to set the count > >> before waking up the task, so compute the cpumask_weight of the > >> resulting AND right before this loop. > >> > >>> + for_each_cpu_and(cpu, &ii_dev->cpumask, cpu_online_mask) { > >>> + iit = per_cpu_ptr(&idle_injection_thread, cpu); > >>> + iit->should_run = 1; > >>> + wake_up_process(iit->tsk); > >>> + } > > > > > > Ah, I see, but since you do: > > > > if (atomic_dec_and_test()) > > last_man() > > > > where that last_man() thing will start a timer, there is no real problem > > with doing atomic_inc() with before wake_up_process(). > > Viresh was worried about the scenario: > > https://lkml.org/lkml/2018/6/5/276 Ah, but I think you have more races, for instance look at wakeup vs park, what if wakeup sets should_run after you've just checked it? Then you have an inc without a dec. > > Also, last_man() uses @run_duration, but the way I read it, the timer is > > for waking things up again, this means it is in fact the sleep duration, > > no? > > No, it is the next idle injection deadline, meanwhile we let the system > continue running. > > The sleep duration is managed by another timer in play_idle(). No, that's the idle duration. Maybe avoid the issue entire by having a {period,idle} tuple, where your old run := period - idle. > > Furthermore, should you not be using hrtimer_forward(&timer, > > idle_duration + run_duration) instead? AFAICT the current scheme is > > prone to drifting. > > (I assume you meant setting the timer in the wakeup task function). > > Yes, drifting is not an issue if that happens. This scheme is simpler > and safer than setting the timer ahead before waking up the tasks with > the risk it expires before all the tasks ended their idle cycles. sloppy though..