From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754785Ab1CVUDg (ORCPT ); Tue, 22 Mar 2011 16:03:36 -0400 Received: from relay3.sgi.com ([192.48.152.1]:59517 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753775Ab1CVUDd (ORCPT ); Tue, 22 Mar 2011 16:03:33 -0400 Date: Tue, 22 Mar 2011 15:02:34 -0500 From: Jack Steiner To: Don Zickus Cc: Cyrill Gorcunov , Ingo Molnar , tglx@linutronix.de, hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra Subject: Re: [PATCH] x86, UV: Fix NMI handler for UV platforms Message-ID: <20110322200234.GA10441@sgi.com> References: <20110321160135.GA31562@sgi.com> <20110321161425.GC23614@elte.hu> <4D877C4B.9090602@gmail.com> <20110321175110.GL1239@redhat.com> <20110321182235.GA14562@sgi.com> <20110321193740.GN1239@redhat.com> <20110322171118.GA6294@sgi.com> <20110322184450.GU1239@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110322184450.GU1239@redhat.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 22, 2011 at 02:44:50PM -0400, Don Zickus wrote: > On Tue, Mar 22, 2011 at 12:11:18PM -0500, Jack Steiner wrote: > > How certain are you that multiple NMIs triggered at about the same time will > > deliver discrete NMI events? I updated the patch so that I'm running with: > > I think as long as there isn't more than two (1 active, 1 latched), you > would be ok. A third one looks like it would get dropped. Hmmm. Although extremely unlikely, would that mean that a problem exists if there are 3 NMI sources: ie., kdb/kgdb, hw_perf & UV. > > > > > - no special code in traps.c (I removed the traps.c code that was > > in the patch I posted) > > - used die_notifier for calling the UV nmi handler > > - UV priority is higher than the hw_perf priority > > > > Both hw_perf (perf top) & UV NMIs work correctly under light loads. However, if I > > run for 10 - 15 minutes injecting UV NMIs at a rate of about 30/min, "perf top" > > stops generating output. Strace shows that it continues to poll() but no data > > is received. > > That's a low frequency and it still gets stuck? Yes. Usually take about a minute. The current NMI mechanism from our node controller limits the NMI rate to about 1 every 2 sec for the current config that I'm running on. > > > > > While "perf top" is hung, if I inject an NMI into the system in a way that will NOT > > be consumed by the UV nmi handler, "perf top" resumes output but will stop again after > > a few minutes. > > So that means the PMU set its interrupt bit but the cpu failed to get the > NMI. That is what it looks like. > > > > > > > AFAICT, the UV nmi handler is not consuming extra NMI interrupts. I can't > > rule out that I'm missing something but I don't see it. > > What happens if you put the UV nmi handler below the hw_perf handler in > priority? I assume the DIE_NMIUNKNOWN snippet in the hw_perf handler will > swallow some of the UV NMIs, but more importantly does it still generate > the hang you see? I'll try that although it may be tomorrow AM before I get a chance. > > > > > > > Do you have any ideas or clues??? > > Part of the problem is most of the NMI testing is done with perf and maybe > kgdb. So high frequency NMI sharing is probably exposing more bugs. > > Also is it a problem to move your testing on to the latest upstream code > instead of RHEL-6? Not all the latest NMI work is there. I want to make > sure we are all starting at the same code. :-) Sure. --- jack > > Cheers, > Don > > > > > > > > > > > > > > > > The root cause of the problem is that architecturally, x86 does not > > > > have a way to identifies the source(s) that cause an NMI. If multiple > > > > events occur at about the same time, there is no way that I can see that the > > > > OS can detect it. > > > > > > There are registers we can check to see who owns trigger the NMI (at least > > > for the perf code, the SGI code maybe not, which is why I set it to a > > > lower priority to be a catch-all). > > > > > > I'm not aware of the x86 architecture dropping NMIs, so they should all > > > get processed. It is just a matter of which subsystems get determine if > > > they are the source of the NMI or not. > > > > > > > > > > > > > > > > > My first impression is the skip nmi logic in the perf handler is probably > > > > > accidentally thinking the SGI external nmi is the perf's 'extra' nmi it is > > > > > supposed to skip and thus swallows it. At least that is the impression I > > > > > > > > Agree > > > > > > > > > > > > > get from the RedHat bugzilla which says SGI is running 'perf top', getting > > > > > a hang, then pressing their nmi button to see the stack traces. > > > > > > > > > > Jack, > > > > > > > > > > I worked through a number of these issues upstream and I already talked to > > > > > George and Russ over here at RedHat about working through the issue over > > > > > here with them. They can help me get access to your box to help debug. > > > > > > > > Russ is right down the hall. > > > > > > Great! > > > > > > Cheers, > > > Don