Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756097Ab0HIUC4 (ORCPT ); Mon, 9 Aug 2010 16:02:56 -0400 Received: from mail-ew0-f46.google.com ([209.85.215.46]:52964 "EHLO mail-ew0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755797Ab0HIUCx (ORCPT ); Mon, 9 Aug 2010 16:02:53 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=vDqflKEOi0S/TYNRP189zqH3s8PeqXLcHpcTCsBWEqjvmQZX5dxM14Sr6aetUzMY53 49sMo9ucy63NVUWulk1QTxSvkByb0PSRFCZt3q9nmcRCIc4Wvz7AbYgJk8FY+eAGcfcq y/K2U5MplqecoR7lf79MPS49N9HZ287T5f3Ek= Date: Tue, 10 Aug 2010 00:02:45 +0400 From: Cyrill Gorcunov To: Robert Richter Cc: Don Zickus , Peter Zijlstra , Lin Ming , Ingo Molnar , "fweisbec@gmail.com" , "linux-kernel@vger.kernel.org" , "Huang, Ying" , Yinghai Lu , Andi Kleen Subject: Re: [PATCH] perf, x86: try to handle unknown nmis with running perfctrs Message-ID: <20100809200245.GF6056@lenovo> References: <20100804151858.GB5130@lenovo> <20100804155002.GS3353@redhat.com> <20100804161046.GC5130@lenovo> <20100804162026.GU3353@redhat.com> <20100804163930.GE5130@lenovo> <20100804184806.GL26154@erda.amd.com> <20100804192634.GG5130@lenovo> <20100806065203.GR26154@erda.amd.com> <20100806142131.GA1874@redhat.com> <20100809194829.GB26154@erda.amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100809194829.GB26154@erda.amd.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3144 Lines: 92 On Mon, Aug 09, 2010 at 09:48:29PM +0200, Robert Richter wrote: > On 06.08.10 10:21:31, Don Zickus wrote: > > On Fri, Aug 06, 2010 at 08:52:03AM +0200, Robert Richter wrote: > > > > I was playing around with it yesterday trying to fix this. My idea is > > > to skip an unkown nmi if the privious nmi was a *handled* perfctr > > > > You might want to add a little more logic that says *handled* _and_ had > > more than one perfctr trigger. Most of the time only one perfctr is > > probably triggering, so you might be eating unknown_nmi's needlessly. > > > > Just a thought. > > Yes, that's true. It could be implemented on top of the patch below. > > > > > > nmi. I will probably post an rfc patch early next week. > > Here it comes: > Thanks Robert! Looks good to me, one nit below. > From d2739578199d881ae6a9537c1b96a0efd1cdea43 Mon Sep 17 00:00:00 2001 > From: Robert Richter > Date: Thu, 5 Aug 2010 16:19:59 +0200 > Subject: [PATCH] perf, x86: try to handle unknown nmis with running perfctrs > ... > diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c > index f2da20f..c3cd159 100644 > --- a/arch/x86/kernel/cpu/perf_event.c > +++ b/arch/x86/kernel/cpu/perf_event.c > @@ -1200,12 +1200,16 @@ void perf_events_lapic_init(void) > apic_write(APIC_LVTPC, APIC_DM_NMI); > } > > +static DEFINE_PER_CPU(unsigned int, perfctr_handled); > + > static int __kprobes > perf_event_nmi_handler(struct notifier_block *self, > unsigned long cmd, void *__args) > { > struct die_args *args = __args; > struct pt_regs *regs; > + unsigned int this_nmi; > + unsigned int prev_nmi; > > if (!atomic_read(&active_events)) > return NOTIFY_DONE; > @@ -1214,7 +1218,26 @@ perf_event_nmi_handler(struct notifier_block *self, > case DIE_NMI: > case DIE_NMI_IPI: > break; > - > + case DIE_NMIUNKNOWN: > + /* > + * This one could be our NMI, two events could trigger > + * 'simultaneously' raising two back-to-back NMIs. If > + * the first NMI handles both, the latter will be > + * empty and daze the CPU. > + * > + * So, we drop this unknown NMI if the previous NMI > + * was handling a perfctr. Otherwise we pass it and > + * let the kernel handle the unknown nmi. > + * > + * Note: this could be improved if we drop unknown > + * NMIs only if we handled more than one perfctr in > + * the previous NMI. > + */ > + this_nmi = percpu_read(irq_stat.__nmi_count); > + prev_nmi = __get_cpu_var(perfctr_handled); > + if (this_nmi == prev_nmi + 1) > + return NOTIFY_STOP; > + return NOTIFY_DONE; > default: > return NOTIFY_DONE; > } > @@ -1222,14 +1245,12 @@ perf_event_nmi_handler(struct notifier_block *self, > regs = args->regs; > > apic_write(APIC_LVTPC, APIC_DM_NMI); If only I'm not missing something this apic_write should go up to "case DIE_NMIUNKNOWN" site, no? -- Cyrill -- 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/