From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754814Ab1GFQyX (ORCPT ); Wed, 6 Jul 2011 12:54:23 -0400 Received: from tx2ehsobe004.messaging.microsoft.com ([65.55.88.14]:26619 "EHLO TX2EHSOBE008.bigfish.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752862Ab1GFQyW (ORCPT ); Wed, 6 Jul 2011 12:54:22 -0400 X-SpamScore: -8 X-BigFish: VPS-8(zz1432N98dKzz1202hzzz32i668h839h944h) X-Forefront-Antispam-Report: CIP:163.181.249.108;KIP:(null);UIP:(null);IPVD:NLI;H:ausb3twp01.amd.com;RD:none;EFVD:NLI X-WSS-ID: 0LNX8AD-01-0CG-02 X-M-MSG: Date: Wed, 6 Jul 2011 18:53:57 +0200 From: Robert Richter To: Ingo Molnar CC: Peter Zijlstra , Paul Mackerras , Arnaldo Carvalho de Melo , "linux-kernel@vger.kernel.org" Subject: Re: [RFC] [PATCH] perf: Attaching an event to a specific PMU Message-ID: <20110706165357.GG4590@erda.amd.com> References: <20110703150430.GV4590@erda.amd.com> <1309716271.3282.6.camel@twins> <20110704175927.GZ4590@erda.amd.com> <1309855905.3282.42.camel@twins> <20110705091252.GA5725@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20110705091252.GA5725@elte.hu> User-Agent: Mutt/1.5.21 (2010-09-15) X-OriginatorOrg: amd.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05.07.11 05:12:52, Ingo Molnar wrote: > > * Peter Zijlstra wrote: > > > > Overall, my approach improves the perf design. It adds a better > > > and more intuitve access to perf from user space with clear and > > > common methods and interfaces. Please let me know the concerns > > > you have. > > > > Its redundant, this interface ship has sailed, its not going to > > happen. > > Even if we had the choice, i don't see how a /dev based enumeration > of PMUs is in any way better than a topologically attached set of > PMUs in /sys. > > This kind of structure is nice in principle: > > # ls -l /dev/pmu/ > total 0 > crw-rw---- 1 root root 254, 5 Jul 8 2011 breakpoint > crw-rw---- 1 root root 254, 4 Jul 8 2011 cpu > crw-rw---- 1 root root 254, 6 Jul 8 2011 proto > crw-rw---- 1 root root 254, 1 Jul 8 2011 software > crw-rw---- 1 root root 254, 2 Jul 8 2011 tracepoint > > But it should be done in /sys/. I have to learn yet why /dev is bad and /sys is good... The system topology is always in /sys, also for device nodes. But we can't get a device file descriptor from /sys. I doubt /sys is capable to handle a device use count (need to be checked). We actually must grab the pmu while attaching events to it. And, user space implementation is must easier with /dev (see code in my previous mail). My patch also includes code that creates a device class. It is also visible in /sys/class/pmu/*. -Robert -- Advanced Micro Devices, Inc. Operating System Research Center