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=-4.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 4B857C43441 for ; Mon, 26 Nov 2018 18:41:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 034AC20865 for ; Mon, 26 Nov 2018 18:41:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="kDj6EdeL" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 034AC20865 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.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 S1726282AbeK0Fgx (ORCPT ); Tue, 27 Nov 2018 00:36:53 -0500 Received: from mail.kernel.org ([198.145.29.99]:57010 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725723AbeK0Fgx (ORCPT ); Tue, 27 Nov 2018 00:36:53 -0500 Received: from localhost (lfbn-ncy-1-241-207.w83-194.abo.wanadoo.fr [83.194.85.207]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 34CBA20862; Mon, 26 Nov 2018 18:41:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1543257714; bh=MK9NAaSBFuvSVHoE16CbMipp9ZlKcpWNEmGOqziKQe4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=kDj6EdeLAtoWA6Xgmh+rqrAd58lZC68+jq+GfQym826bFoh0LBGycLsuRAoOEs78Y Lg6JbBCe7HpTTQlXgAxtrTHw/+9dxlypp/lH9Y+R6G8culgsWhp4wt9YGH0OUxogiB BYGjaCyoy47eBudk2KEApOWkejGfLzEfEQKI5LRY= Date: Mon, 26 Nov 2018 19:41:51 +0100 From: Frederic Weisbecker To: Peter Zijlstra Cc: LKML , Wanpeng Li , Thomas Gleixner , Yauheni Kaliuta , Ingo Molnar , Rik van Riel Subject: Re: [PATCH 19/25] sched/vite: Handle nice updates under vtime Message-ID: <20181126184150.GB18962@lerouge> References: <1542163569-20047-1-git-send-email-frederic@kernel.org> <1542163569-20047-20-git-send-email-frederic@kernel.org> <20181120141754.GW2131@hirez.programming.kicks-ass.net> <20181126155352.GA18962@lerouge> <20181126161103.GW2131@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181126161103.GW2131@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 26, 2018 at 05:11:03PM +0100, Peter Zijlstra wrote: > On Mon, Nov 26, 2018 at 04:53:54PM +0100, Frederic Weisbecker wrote: > > > > + irq_work_queue_on(&per_cpu(vtime_set_nice_work, cpu), cpu); > > > > > > What happens if you already had one pending? Do we loose updates? > > > > No, if irq_work is already pending, it doesn't requeue iff the work hasn't > > been executed yet and it's guaranteed it will see the freshest update. > > (you should trust more the code you wrote ;-) > > Yeah, I do remember hoq irq_work works. What I was asking was about how > this specific handler deals with 'missing' updates. > > Suppose we start with state A, set it to B and raise the IPI, then set > it to C before the interrupt happens. > > That means the irq_work handler will see C and never observe B. Ah right, but that's ok, we can miss a few intermediate very short states. In this case the most recent update is the relevant one.