From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758425AbcCVH5q (ORCPT ); Tue, 22 Mar 2016 03:57:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53993 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755811AbcCVH5i (ORCPT ); Tue, 22 Mar 2016 03:57:38 -0400 Date: Tue, 22 Mar 2016 08:57:35 +0100 From: Jiri Olsa To: Andi Kleen Cc: acme@kernel.org, jolsa@kernel.org, mingo@kernel.org, peterz@infradead.org, linux-kernel@vger.kernel.org, Andi Kleen Subject: Re: [PATCH 1/2] perf, tools: Document event specifications better Message-ID: <20160322075735.GA4473@krava.brq.redhat.com> References: <1458575793-12091-1-git-send-email-andi@firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1458575793-12091-1-git-send-email-andi@firstfloor.org> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 21, 2016 at 08:56:32AM -0700, Andi Kleen wrote: SNIP > +EVENT GROUPS > +------------ > + > +Perf supports time based multiplexing of events, when the number of events > +active exceeds the number of hardware performance counters. Multiplexing > +can cause measurement errors when the workload changes its execution > +profile. > + > +When metrics are computed using formulas from event counts, it is useful to > +ensure some events are always measured together as a group to minimize multiplexing > +errors. Event groups can be specified using { }. > + > + perf stat -e '{instructions,cycles}' ... > + > +When too many events are specified in the group perf the event will not ^^^^^^^^^^^^^^ maybe: 'none of them' will be meassured. > +be measured. The number of available performance counters depend on the CPU. > +For example Intel Core CPUs have typically four generic performance counters > +for the core, plus a number of specialized fixed counters. > + > +Events from multiple different PMUs cannot be mixed in a group. hum, but we allow that right? only when there's mixture of SW and HW events we move it all silently under HW event context jirka