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=-0.8 required=3.0 tests=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 42D3FC33CAF for ; Thu, 16 Jan 2020 19:10:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 110E5206E6 for ; Thu, 16 Jan 2020 19:10:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2437537AbgAPTKg convert rfc822-to-8bit (ORCPT ); Thu, 16 Jan 2020 14:10:36 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:53049 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2437450AbgAPTK2 (ORCPT ); Thu, 16 Jan 2020 14:10:28 -0500 Received: from p5b06da22.dip0.t-ipconnect.de ([91.6.218.34] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1isAX2-0007HG-TQ; Thu, 16 Jan 2020 20:10:17 +0100 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 5F3FB101226; Thu, 16 Jan 2020 20:10:16 +0100 (CET) From: Thomas Gleixner To: Waiman Long , Robert Richter Cc: Andrew Morton , Ingo Molnar , "linux-kernel\@vger.kernel.org" , Mike Rapoport , Kees Cook , Catalin Marinas , Will Deacon , Peter Zijlstra Subject: Re: [PATCH v2] watchdog: Fix possible soft lockup warning at bootup In-Reply-To: <9ae2ee4d-7b67-50ff-e736-1d51753c5ccd@redhat.com> Date: Thu, 16 Jan 2020 20:10:16 +0100 Message-ID: <87ftgffc9z.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Waiman Long writes: > On 1/16/20 11:57 AM, Thomas Gleixner wrote: >>> So your theory the MONOTONIC clock runs differently/wrongly could >>> explain that (assuming this drives the sched clock). Though, I am >> No. sched_clock() is separate. It uses a raw timestamp (in your case >> from the ARM arch timer) and converts it to something which is close to >> proper time. So my assumption was based on the printout Waiman had: >> >> [ 1... ] CPU.... watchdog_fn now 170000000 >> [ 25.. ] CPU.... watchdog_fn now 4170000000 >> >> I assumed that now comes from ktime_get() or something like >> that. Waiman? > > I printed out the now parameter of the  __hrtimer_run_queues() call. Yes. That's clock MONOTONIC. > So from the timer perspective, it is losing time. For watchdog, the soft > expiry time is 4s. The watchdog function won't be called until the > timer's time advances 4s or more. That corresponds to about 24s in > timestamp time for that particular class of systems. Right. And assumed that the firmware call is the culprit this has an explanation. Could you please take sched_clock() timestamps before and after the firmware call which kicks the secondary CPUs into life to verify that? They should sum up to the amount of time which gets lost accross smp_init(). Thanks, tglx