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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,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 46F82C43603 for ; Wed, 11 Dec 2019 20:37:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1A01D206A5 for ; Wed, 11 Dec 2019 20:37:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="gO/JxjeH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727729AbfLKUho (ORCPT ); Wed, 11 Dec 2019 15:37:44 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:25645 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726242AbfLKUhn (ORCPT ); Wed, 11 Dec 2019 15:37:43 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1576096662; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2vDUOH0NL2++sNq8ly9oZ+vSwQKreWmMi7WXNmKRknE=; b=gO/JxjeHYpoyEnAbhNmsd/ztYVfT8wP6MP48oMUQR2CIT4h6puOdnUjSIaqJbFGM+kulXa EydpJcoW/yo5sSog5gPMBZXQPGsyMV+79MAEWYgJDakEQcAmWZOT4b/kHmPQqxYRvg5PKR veCYIJcpb0hD/sZsfo3OxUDc5IjAfXA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-261-6yr6dRIEPVy6laS1jeqZIA-1; Wed, 11 Dec 2019 15:37:38 -0500 X-MC-Unique: 6yr6dRIEPVy6laS1jeqZIA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7DD9C18AAFC9; Wed, 11 Dec 2019 20:37:37 +0000 (UTC) Received: from ovpn-116-192.phx2.redhat.com (ovpn-116-192.phx2.redhat.com [10.3.116.192]) by smtp.corp.redhat.com (Postfix) with ESMTP id EB32D5C219; Wed, 11 Dec 2019 20:37:36 +0000 (UTC) Message-ID: Subject: Re: [PATCH] timers/nohz: Update nohz load even if tick already stopped From: Scott Wood To: Peter Zijlstra Cc: Thomas Gleixner , Frederic Weisbecker , Ingo Molnar , LKML In-Reply-To: References: <20191028150716.22890-1-frederic@kernel.org> <20191029100506.GJ4114@hirez.programming.kicks-ass.net> <52d963553deda810113accd8d69b6dffdb37144f.camel@redhat.com> <20191030133130.GY4097@hirez.programming.kicks-ass.net> <813ed21938aa47b15f35f8834ffd98ad4dd27771.camel@redhat.com> <7b782bc880a29eb7d37f2c2aff73c43e7f7d032f.camel@redhat.com> <20191105124351.GN4131@hirez.programming.kicks-ass.net> Organization: Red Hat Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 Date: Wed, 11 Dec 2019 14:37:05 -0600 User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2019-11-08 at 02:13 -0600, Scott Wood wrote: > On Tue, 2019-11-05 at 13:43 +0100, Peter Zijlstra wrote: > > On Tue, Nov 05, 2019 at 01:30:58AM -0600, Scott Wood wrote: > > > As for the warning in sched_tick_remote(), it seems like a test for > > > time > > > since the last tick on this cpu (remote or otherwise) would be better > > > than > > > relying on curr->se.exec_start, in order to detect things like this. > > > > I don't think we have a timestamp that is shared between the remote and > > local tick. > > Why wouldn't rq_clock_task() work on the local tick? It's what > ->task_tick() itself uses. > > > Also, there is a reason this warning uses the task time > > accounting, there used to be (as in, I can't find it in a hurry) code > > that could not deal with >u32 (~4s) clock updates. > > Detecting a 3 second interval between ticks for a given cpu should > assert in a superset of the situations the current check asserts in -- > it just avoids the false negative of exec_runtime getting updated by > something other than the tick. The main difficulty with such a check is that when we're not on a full nohz cpu, there's no remote tick, and so we can legitimately go more than 3 seconds between ticks when idle. -Scott