Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752402Ab3IJP3C (ORCPT ); Tue, 10 Sep 2013 11:29:02 -0400 Received: from merlin.infradead.org ([205.233.59.134]:49936 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751387Ab3IJP3B (ORCPT ); Tue, 10 Sep 2013 11:29:01 -0400 Date: Tue, 10 Sep 2013 17:28:45 +0200 From: Peter Zijlstra To: eranian@gmail.com Cc: Ingo Molnar , Linus Torvalds , Linux Kernel Mailing List , Arnaldo Carvalho de Melo , Thomas Gleixner , Andi Kleen Subject: Re: PEBS bug on HSW: "Unexpected number of pebs records 10" (was: Re: [GIT PULL] perf changes for v3.12) Message-ID: <20130910152845.GI31370@twins.programming.kicks-ass.net> References: <20130903132933.GA24955@gmail.com> <20130909100544.GI31370@twins.programming.kicks-ass.net> <20130910115306.GA6091@gmail.com> <20130910133845.GB7537@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1217 Lines: 24 On Tue, Sep 10, 2013 at 07:15:19AM -0700, Stephane Eranian wrote: > The threshold is where to generate the interrupt. It does not mean > where to stop PEBS recording. It does, since we don't set a reset value. So once a PEBS assist happens, that counter stops until we reprogram it in the PMI. > So it is possible that in HSW, we may > get into a situation where it takes time to get to the handler to stop > the PMU. I don't know how given we use NMI. Well, unless we were > already servicing an NMI at the time. But given that we stop the PMU > almost immediately in the handler, I don't see how that would > possible. The other oddity in HSW is that we clear the NMI on entry > to the handler and not at the end. I never gotten an good explanation > as to why that was necessary. So maybe it is related... Even if the PMI was delayed that counter would never do another entry. So I really don't see how we can have more than nr_counters PEBS entries in the buffer. -- 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/