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=-2.4 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,USER_AGENT_SANE_1 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 E2BE0C33CAF for ; Thu, 16 Jan 2020 19:14:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BDBCA2072E for ; Thu, 16 Jan 2020 19:14:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="YjWDNDUN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2437245AbgAPTOC (ORCPT ); Thu, 16 Jan 2020 14:14:02 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:47507 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2437490AbgAPTN5 (ORCPT ); Thu, 16 Jan 2020 14:13:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579202036; 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=dfJAU7RaHy4HkG5bX3qzQ3Wzr16UrjmMEFK9k1V7IkQ=; b=YjWDNDUNaEK3ir3JdxHeu1DbYBW0GcyEZ4EtpIAngmxICCqN4agf+V4c/l/9lizUqMusYy 76aE9S5GY/SjKDdUvf5pV6LqmHuvCvXtFdsPUvbok5OvFatwfW+j7P6EZRr0U8ocJf6N7o lYhTcfwkJ7rCPnprRj/uCkEOEAqiJQo= 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-412-_pqLLkqMPlaIidvTIzRJPg-1; Thu, 16 Jan 2020 14:13:52 -0500 X-MC-Unique: _pqLLkqMPlaIidvTIzRJPg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C7299107ACC7; Thu, 16 Jan 2020 19:13:50 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-59.bos.redhat.com [10.18.17.59]) by smtp.corp.redhat.com (Postfix) with ESMTP id 923CC60C63; Thu, 16 Jan 2020 19:13:49 +0000 (UTC) Subject: Re: [PATCH v2] watchdog: Fix possible soft lockup warning at bootup To: Thomas Gleixner , Robert Richter Cc: Andrew Morton , Ingo Molnar , "linux-kernel@vger.kernel.org" , Mike Rapoport , Kees Cook , Catalin Marinas , Will Deacon , Peter Zijlstra References: <87ftgffc9z.fsf@nanos.tec.linutronix.de> From: Waiman Long Organization: Red Hat Message-ID: <7168b0aa-4904-4246-0de5-3906df13b5c8@redhat.com> Date: Thu, 16 Jan 2020 14:13:49 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <87ftgffc9z.fsf@nanos.tec.linutronix.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/16/20 2:10 PM, Thomas Gleixner wrote: > 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=C2=A0 __hrtimer_run_queues() ca= ll. > Yes. That's clock MONOTONIC. > >> So from the timer perspective, it is losing time. For watchdog, the so= ft >> 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(). Sure, I will do that after I get hold of the arm64 system that can reproduce the issue. That system is currently used by another engineer. Cheers, Longman