From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753323AbaIBJob (ORCPT ); Tue, 2 Sep 2014 05:44:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:15283 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750903AbaIBJoa (ORCPT ); Tue, 2 Sep 2014 05:44:30 -0400 Date: Tue, 2 Sep 2014 11:17:44 +0200 From: Jiri Olsa To: Adrian Hunter Cc: Arnaldo Carvalho de Melo , Peter Zijlstra , linux-kernel@vger.kernel.org, David Ahern , Frederic Weisbecker , Namhyung Kim , Paul Mackerras , Stephane Eranian Subject: Re: [PATCH 20/41] perf tools: Let a user specify a PMU event without any config terms Message-ID: <20140902091744.GC8044@krava.redhat.com> References: <1405332185-4050-1-git-send-email-adrian.hunter@intel.com> <1405332185-4050-21-git-send-email-adrian.hunter@intel.com> <20140716142510.GE9441@krava.redhat.com> <53C6948C.2080103@intel.com> <20140716182214.GB32716@krava.redhat.com> <5400CB13.4040004@intel.com> <20140830085310.GA14358@krava.redhat.com> <540411C5.8030207@intel.com> <20140901191107.GE1900@krava.redhat.com> <5405582C.6070402@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5405582C.6070402@intel.com> 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 On Tue, Sep 02, 2014 at 08:39:56AM +0300, Adrian Hunter wrote: SNIP > >>> -e intel_pt/tsc=1,noretcomp=0/ > >>> > >>> I guess I wanted to hear more elaboration why is this better > >>> than the current way we have by defining an alias, like: > >>> > >>> krava alias: "tsc=1,noretcomp=0" > >>> > >>> -e intel_pt/krava/ > >>> > >>> which gives the same result > >> > >> The default value must be provided by perf tools not the kernel e.g. > >> an older version of perf tools will not be aware of new hardware > >> features that the kernel may know about. If the kernel enables > >> new features by default then the tool may fail. Thus the default > >> value has to be under the control of the tools not the kernel, so > >> a sysfs alias will not work. > >> > > > > I dont follow, could u provide some example? > > Imagine that the 'tsc' term did not exist. Intel PT trace data > would not contain TSC packets, and the decoder would not know how to > decode them. Then imagine that a new version of the hardware adds > 'tsc'. It is such a useful feature that we want it by default, but > older versions of the tools don't know how to decode it, so the > kernel cannot turn it on by default. > > > > > why the tool needs to understand.. it will just take the alias > > and apply/use it? The alias follows the format logic, which tells > > how to apply values on perf_event_attr.. and the kernel knows best > > what's supported in its version.. > > It is similar to why the kernel does not select mmap2 by default. The > kernel doesn't know whether the tool supports it. > ook, could you please add some kind of this explanation to the changelog? thanks, jirka