From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: [PATCH 3/4] x86/nmi: wait for all CPUs in check_nmi_watchdog() Date: Wed, 14 May 2014 14:59:58 +0100 Message-ID: <537392FE02000078000123AD@mail.emea.novell.com> References: <1400072299-2285-1-git-send-email-david.vrabel@citrix.com> <1400072299-2285-4-git-send-email-david.vrabel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1WkZiz-0002OA-Qx for xen-devel@lists.xenproject.org; Wed, 14 May 2014 14:00:03 +0000 In-Reply-To: <1400072299-2285-4-git-send-email-david.vrabel@citrix.com> Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: David Vrabel Cc: xen-devel@lists.xenproject.org, Keir Fraser List-Id: xen-devel@lists.xenproject.org >>> On 14.05.14 at 14:58, wrote: > The counting of a CPUs NMIs in check_nmi_watchdog() is only reliable > if all CPUs have been spinning for 5 or more ticks. There may be > delays in waking other CPUs from deep power states that can mean that > when the counts are checked CPUs haven't run for long enough. 5 ticks ought to be a couple of orders of a magnitude longer than the worst possible wakeup time. I.e. I don't buy this argument without actual numbers to support it. Jan