From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754762AbZFXHIP (ORCPT ); Wed, 24 Jun 2009 03:08:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751973AbZFXHII (ORCPT ); Wed, 24 Jun 2009 03:08:08 -0400 Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:39986 "EHLO sunset.davemloft.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751444AbZFXHIH (ORCPT ); Wed, 24 Jun 2009 03:08:07 -0400 Date: Wed, 24 Jun 2009 00:08:11 -0700 (PDT) Message-Id: <20090624.000811.118222188.davem@davemloft.net> To: andi@firstfloor.org Cc: linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org Subject: Re: NMI watchdog + NOHZ question From: David Miller In-Reply-To: <20090624070315.GH6760@one.firstfloor.org> References: <20090622.022752.219499742.davem@davemloft.net> <20090623.171735.154729801.davem@davemloft.net> <20090624070315.GH6760@one.firstfloor.org> X-Mailer: Mew version 6.2.51 on Emacs 22.1 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andi Kleen Date: Wed, 24 Jun 2009 09:03:15 +0200 >> I'm not exactly sure what to do about this. > > Ack the timer interrupt earlier (and also give it a high priority?) It has a higher priority, but all interrupts get re-enabled right before we process software interrupts. So the flood of qla2xxx interrupts can come in before we can run the timer softirq and thus schedule the next timer interrupt. > That could be still problematic if you have non nestabled irq stacks > (haven't checked if sparc has that or not), > potentially you might need to run the softirq on the process stack. IRQ stacks on sparc64 work identically to how they do on x86. I have some more theories about this, in that I always see the NMI watchdog message with a PC right in the section of CPU idle where NOHZ is enabled. On these cpus there is no support yielding, so on them I just touch the NMI watchdog in the loop waiting for need_resched() to become true. But if we get the qla2xxx interrupt storm during that loop, it's pretty easy to not touch the NMI watchdog in time.