From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754065AbcIVH4K (ORCPT ); Thu, 22 Sep 2016 03:56:10 -0400 Received: from merlin.infradead.org ([205.233.59.134]:44570 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752680AbcIVH4J (ORCPT ); Thu, 22 Sep 2016 03:56:09 -0400 Date: Thu, 22 Sep 2016 09:56:03 +0200 From: Peter Zijlstra To: Paul Clarke Cc: Vineet Gupta , "linux-perf-users@vger.kernel.org" , Alexey Brodkin , Will Deacon , "linux-kernel@vger.kernel.org" , Arnaldo Carvalho de Melo , "linux-snps-arc@lists.infradead.org" , Jiri Olsa Subject: Re: perf event grouping for dummies (was Re: [PATCH] arc: perf: Enable generic "cache-references" and "cache-misses" events) Message-ID: <20160922075603.GW5008@twins.programming.kicks-ass.net> References: <1472125647-518-1-git-send-email-abrodkin@synopsys.com> <6074e252-6e18-bb01-4de1-023bd7e82f03@synopsys.com> <5f65fa04-8d33-e525-115d-4e6991a7668e@synopsys.com> <20160901083324.GM10153@twins.programming.kicks-ass.net> <2a18ae06-3abd-c3a1-e980-f04c511b08e5@synopsys.com> <04f6dcd2-35c6-6e28-2dcf-bc5f0bb446dc@us.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <04f6dcd2-35c6-6e28-2dcf-bc5f0bb446dc@us.ibm.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 21, 2016 at 07:43:28PM -0500, Paul Clarke wrote: > On 09/20/2016 03:56 PM, Vineet Gupta wrote: > >On 09/01/2016 01:33 AM, Peter Zijlstra wrote: > >>>- is that what perf event grouping is ? > >> > >>Again, nope. Perf event groups are single counter (so no implicit > >>addition) that are co-scheduled on the PMU. > > > >I'm not sure I understand - does this require specific PMU/arch support - as in > >multiple conditions feeding to same counter. > > My read is that is that what Peter meant was that each event in the > perf event group is a single counter, so all the events in the group > are counted simultaneously. (No multiplexing.) Right, sorry for the poor wording. > >Again when you say co-scheduled what do you mean - why would anyone use the event > >grouping - is it when they only have 1 counter and they want to count 2 > >conditions/events at the same time - isn't this same as event multiplexing ? > > I'd say it's the converse of multiplexing. Instead of mapping > multiple events to a single counter, perf event groups map a set of > events each to their own counter, and they are active simultaneously. > I suppose it's possible for the _groups_ to be multiplexed with other > events or groups, but the group as a whole will be scheduled together, > as a group. Correct. Each events get their own hardware counter. Grouped events are co-scheduled on the hardware. You can multiplex groups. But if one event in a group is schedule, they all must be.