From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754969AbaEIHK5 (ORCPT ); Fri, 9 May 2014 03:10:57 -0400 Received: from mail-ee0-f45.google.com ([74.125.83.45]:55517 "EHLO mail-ee0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754274AbaEIHKz (ORCPT ); Fri, 9 May 2014 03:10:55 -0400 Date: Fri, 9 May 2014 09:10:50 +0200 From: Ingo Molnar To: Don Zickus Cc: x86@kernel.org, Peter Zijlstra , ak@linux.intel.com, gong.chen@linux.intel.com, LKML , Thomas Gleixner , =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , Steven Rostedt , andi@firstfloor.org Subject: Re: [PATCH 1/5] x86, nmi: Add new nmi type 'external' Message-ID: <20140509071050.GA19751@gmail.com> References: <1399476883-98970-1-git-send-email-dzickus@redhat.com> <1399476883-98970-2-git-send-email-dzickus@redhat.com> <20140507153854.GA14926@gmail.com> <20140507160251.GQ39568@redhat.com> <20140507162746.GA15779@gmail.com> <20140508163333.GZ39568@redhat.com> <20140508173501.GA9838@gmail.com> <20140508175247.GA39568@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140508175247.GA39568@redhat.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 * Don Zickus wrote: > On Thu, May 08, 2014 at 07:35:01PM +0200, Ingo Molnar wrote: > > > > * Don Zickus wrote: > > > > > > > Again, I don't have a solution to juggle between PMI performance > > > > > and reliable delivery. We could do away with the spinlocks and > > > > > go back to single cpu delivery (like it used to be). Then > > > > > devise a mechanism to switch delivery to another cpu upon > > > > > hotplug. > > > > > > > > > > Thoughts? > > > > > > > > I'd say we should do a delayed timer that makes sure that all > > > > possible handlers are polled after an NMI is triggered, but never > > > > at a high rate. > > > > > > Hmm, I was thinking about it and wanted to avoid a poll as I hear > > > complaints here and there about the nmi_watchdog constantly wasting > > > power cycles with its polling. > > > > But the polling would only happen if there's NMI traffic, so that's > > fine. So as long as polling stops some time after the last PMI use, > > it's a good solution. > > So you are thinking an NMI comes in, kicks off a delayed timer for > say 10ms. The timer fires, rechecks the NMI for missed events and > then stops? If another NMI happens before the timer fires, just kick > the timer again? > > Something like that? Yeah, exactly, using delayed IRQ work for that or so. This would allow us to 'optimistic' processing of NMI events: the first handler that manages to do any work causes a return. No need to make a per handler distinction, etc. It would generally be pretty robust and would possibly be a natural workaround for 'stuck PMU' type of bugs as well. [ As long as it does not result in spurious 'dazed and confused' messages :-) ] Thanks, Ingo