Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932199AbbETQZS (ORCPT ); Wed, 20 May 2015 12:25:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49862 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932164AbbETQZP (ORCPT ); Wed, 20 May 2015 12:25:15 -0400 Date: Wed, 20 May 2015 18:25:10 +0200 From: Jiri Olsa To: Peter Zijlstra Cc: Vince Weaver , LKML , Stephane Eranian , Arnaldo Carvalho de Melo , Ingo Molnar , Paul Mackerras Subject: Re: perf: odd event scheduling issue Message-ID: <20150520162510.GA16635@krava.redhat.com> References: <20150520070057.GK3644@twins.programming.kicks-ass.net> <20150520092842.GF18673@twins.programming.kicks-ass.net> <20150520135209.GI18673@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150520135209.GI18673@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2544 Lines: 58 On Wed, May 20, 2015 at 03:52:09PM +0200, Peter Zijlstra wrote: > On Wed, May 20, 2015 at 11:28:42AM +0200, Peter Zijlstra wrote: > > > --- > > > > c02cdbf60b51b8d98a49185535f5d527a2965142 is the first bad commit > > commit c02cdbf60b51b8d98a49185535f5d527a2965142 > > Author: Stephane Eranian > > Date: Mon Nov 17 20:07:02 2014 +0100 > > > > perf/x86/intel: Limit to half counters when the HT workaround is enabled, to avoid exclusive mode starvation > > > > This patch limits the number of counters available to each CPU when > > the HT bug workaround is enabled. > > > > This is necessary to avoid situation of counter starvation. Such can > > arise from configuration where one HT thread, HT0, is using all 4 counters > > with corrupting events which require exclusion the the sibling HT, HT1. > > > > In such case, HT1 would not be able to schedule any event until HT0 > > is done. To mitigate this problem, this patch artificially limits > > the number of counters to 2. > > > > That way, we can gurantee that at least 2 counters are not in exclusive > > mode and therefore allow the sibling thread to schedule events of the > > same type (system vs. per-thread). The 2 counters are not determined > > in advance. We simply set the limit to two events per HT. > > > > This helps mitigate starvation in case of events with specific counter > > constraints such a PREC_DIST. > > > > Note that this does not elimintate the starvation is all cases. But > > it is better than not having it. > > > > (Solution suggested by Peter Zjilstra.) > > > > Signed-off-by: Stephane Eranian > > Signed-off-by: Peter Zijlstra (Intel) > > Cc: bp@alien8.de > > Cc: jolsa@redhat.com > > Cc: kan.liang@intel.com > > Cc: maria.n.dimakopoulou@gmail.com > > Link: http://lkml.kernel.org/r/1416251225-17721-11-git-send-email-eranian@google.com > > Signed-off-by: Ingo Molnar > > OK, so if you have the watchdog enabled, that's 1 event, and having a > max of 2 GP events, adding another 2 events is fail. > > Jiri, did you SNB have the watchdog disabled? watchdog was enabled jirka -- 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/