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=-2.3 required=3.0 tests=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 7817ECA9EAF for ; Mon, 21 Oct 2019 13:04:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 52BB620679 for ; Mon, 21 Oct 2019 13:04:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728837AbfJUNE2 (ORCPT ); Mon, 21 Oct 2019 09:04:28 -0400 Received: from mx2.suse.de ([195.135.220.15]:34558 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727256AbfJUNE1 (ORCPT ); Mon, 21 Oct 2019 09:04:27 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 1C783B504; Mon, 21 Oct 2019 13:04:26 +0000 (UTC) Date: Mon, 21 Oct 2019 15:04:25 +0200 From: Petr Mladek To: Peter Zijlstra Cc: Thomas Gleixner , Ingo Molnar , Laurence Oberman , Vincent Whitchurch , Michal Hocko , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] watchdog/softlockup: Preserve original timestamp when touching watchdog externally Message-ID: <20191021130425.ewiegm2425hkydb3@pathway.suse.cz> References: <20190819104732.20966-1-pmladek@suse.com> <20190819104732.20966-2-pmladek@suse.com> <20191021124214.GD1817@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191021124214.GD1817@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20170912 (1.9.0) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 2019-10-21 14:42:14, Peter Zijlstra wrote: > On Mon, Aug 19, 2019 at 12:47:30PM +0200, Petr Mladek wrote: > > Some bug report included the same softlockups in flush_tlb_kernel_range() > > in regular intervals. Unfortunately was not clear if there was a progress > > or not. > > > > The situation can be simulated with a simply busy loop: > > > > while (true) > > cpu_relax(); > > > > The softlockup detector produces: > > > > [ 168.277520] watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [cat:4865] > > [ 196.277604] watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [cat:4865] > > [ 236.277522] watchdog: BUG: soft lockup - CPU#1 stuck for 23s! [cat:4865] > > > > One would expect only one softlockup report or several reports with > > an increased duration. > > Let's just say our expectations differ. > > > The result is that each softlockup is reported only once unless > > another process get scheduled: > > > > [ 320.248948] watchdog: BUG: soft lockup - CPU#2 stuck for 26s! [cat:4916] > > Which would greatly confuse me; as the above would have me think the > situation got resolved (no more lockups reported) even though it is > still very much stuck there. > > IOW, I don't see how this makes anything better. You're removing > information. The 2nd patch brings back the regular report but with correctly counted time (stuck for XXs). I split it into two patches because I was not sure what would be preferred behavior. I prefer the regular reports as well. Best Regards, Petr