Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754672Ab3DVS7s (ORCPT ); Mon, 22 Apr 2013 14:59:48 -0400 Received: from mx1.redhat.com ([209.132.183.28]:2872 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754544Ab3DVS7r (ORCPT ); Mon, 22 Apr 2013 14:59:47 -0400 Date: Mon, 22 Apr 2013 14:59:29 -0400 From: Don Zickus To: "Pan, Zhenjie" Cc: Stephane Eranian , Peter Zijlstra , "paulus@samba.org" , "mingo@redhat.com" , "acme@ghostprotocols.net" , "akpm@linux-foundation.org" , "tglx@linutronix.de" , "Liu, Chuansheng" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v2] NMI: fix NMI period is not correct when cpu frequency changes issue. Message-ID: <20130422185929.GZ79013@redhat.com> References: <1366285369.19383.19.camel@laptop> <20130418133927.GJ79013@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Content-Length: 1496 Lines: 32 On Mon, Apr 22, 2013 at 12:50:34AM +0000, Pan, Zhenjie wrote: > > I believe it mattered to the Chrome folks. They want the watchdog to be as > > tight as possible so the user experience isn't a hang but a quick reboot > > instead. They like setting the watchdog to something like 2 seconds. > > > > There was a patch a few months ago that tried to hack around this issue and I > > suggested this approach as a better solution. I forgot what the original > > problem was. Perhaps someone can jump in and explain the problem being > > solved (other than the watchdog isn't always 10 seconds)? > > > > Cheers, > > Don > > Yes, I also think the period is important sometimes. > As I mentioned before, the case I meet is: > When the system hang with interrupt disabled, we use NMI to detect. > Then it will find hard lockup and cause a panic. > Panic is very important for debug these kind of issues. > > But if cpu frequency change, the period will be 2 times, 3 times even more.(if cpu can down from 2.0GHz to 200MHz, will be 10 times, it's a very big deviation) > This make watchdog reset happen before hard lockup detect. So you are saying with the longer hard lockup delay, the iTCO_wdt is firing before the hard lockup detector? Cheers, Don -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/