From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752164AbaHRSnv (ORCPT ); Mon, 18 Aug 2014 14:43:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49838 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751676AbaHRSnt (ORCPT ); Mon, 18 Aug 2014 14:43:49 -0400 Date: Mon, 18 Aug 2014 14:43:43 -0400 From: Don Zickus To: Ingo Molnar Cc: akpm@linux-foundation.org, kvm@vger.kernel.org, pbonzini@redhat.com, mingo@redhat.com, LKML , chai wen Subject: Re: [PATCH 2/5] softlockup: make detector be aware of task switch of processes hogging cpu Message-ID: <20140818184339.GB49576@redhat.com> References: <1407768567-171794-1-git-send-email-dzickus@redhat.com> <1407768567-171794-3-git-send-email-dzickus@redhat.com> <20140818090319.GA25495@gmail.com> <20140818150658.GQ49576@redhat.com> <20140818180158.GA4540@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140818180158.GA4540@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 18, 2014 at 08:01:58PM +0200, Ingo Molnar wrote: > > > > duration = is_softlockup(touch_ts); > > > > if (unlikely(duration)) { > > > > + pid_t pid = task_pid_nr(current); > > > > + > > > > /* > > > > * If a virtual machine is stopped by the host it can look to > > > > * the watchdog like a soft lockup, check to see if the host > > > > @@ -326,8 +329,20 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) > > > > return HRTIMER_RESTART; > > > > > > > > /* only warn once */ > > > > - if (__this_cpu_read(soft_watchdog_warn) == true) > > > > + if (__this_cpu_read(soft_watchdog_warn) == true) { > > > > + > > > > + /* > > > > + * Handle the case where multiple processes are > > > > + * causing softlockups but the duration is small > > > > + * enough, the softlockup detector can not reset > > > > + * itself in time. Use pids to detect this. > > > > + */ > > > > + if (__this_cpu_read(softlockup_warn_pid_saved) != pid) { > > > > > > So I agree with the motivation of this improvement, but is this > > > implementation namespace-safe? > > > > What namespace are you worried about colliding with? I thought > > softlockup_ would provide the safety?? Maybe I am missing something > > obvious. :-( > > I meant PID namespaces - a PID in itself isn't guaranteed to be > unique across the system. Ah, I don't think we thought about that. Is there a better way to do this? Is there a domain id or something that can be OR'd with the pid? Cheers, Don