From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752762Ab1GUIQQ (ORCPT ); Thu, 21 Jul 2011 04:16:16 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:38540 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752503Ab1GUIQP (ORCPT ); Thu, 21 Jul 2011 04:16:15 -0400 Date: Thu, 21 Jul 2011 10:15:31 +0200 From: Ingo Molnar To: Cyrill Gorcunov Cc: Peter Zijlstra , Don Zickus , LKML , Stephane Eranian , Lin Ming , Arnaldo Carvalho de Melo , Frederic Weisbecker , Steven Rostedt Subject: Re: [PATCH -tip/perf/core] perf, x86: P4 PMU - Introduce event alias feature Message-ID: <20110721081531.GI9216@elte.hu> References: <20110708201712.GS23657@sun> <20110721064610.GB26260@elte.hu> <20110721072052.GM7492@sun> <20110721075201.GH9216@elte.hu> <20110721080755.GO7492@sun> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110721080755.GO7492@sun> User-Agent: Mutt/1.5.21 (2010-09-15) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Cyrill Gorcunov wrote: > On Thu, Jul 21, 2011 at 09:52:01AM +0200, Ingo Molnar wrote: > > > > * Cyrill Gorcunov wrote: > > > > > > > +static u64 p4_get_alias_event(u64 config) > > > > > +{ > > > > > + u64 config_match; > > > > > + int i; > > > > > + > > > > > + /* > > > > > + * Probably we're lucky and don't have to do > > > > > + * matching over all config bits. > > > > > + */ > > > > > + if (!(config & P4_CONFIG_ALIASABLE)) > > > > > + return 0; > > > > > > > > 'all' config bits? There's a single alias mapping in > > > > p4_event_aliases[] right now which makes the comment rather > > > > misleading ... > > > > > > no, the cycle below does check for all bits in config, and test > > > for single bit might help us to return early. > > > > The loop below? AFAICS it does: > > > > > > > + */ > > > > > + for (i = 0; i < ARRAY_SIZE(p4_event_aliases); i++) { > > > > > + if (config_match == p4_event_aliases[i].orig) { > > > > > + config_match = p4_event_aliases[i].alter; > > > > > + break; > > > > > + } else if (config_match == p4_event_aliases[i].alter) { > > > > > + config_match = p4_event_aliases[i].orig; > > > > > + break; > > > > > + } > > > > > + } > > > > and p4_event_aliases[] is a single-entry array, so ARRAY_SIZE() is 1 > > and this loop iterates once. > > I know, but Ingo, I can't guarantee that we'll never bring some new > alias(es) later ;) [...] in which 'later' case that check and the comment can be added or updated ... Right now it looks both somewhat pointless *and* the comment is somewhat misleading. You could fix the comment, pointing out that right now it's only a single entry but it's still a micro-optimization. and if there's more entries in the future the comment can be updated. > > > > Since this .c file is P4 specific and p4_event_aliases[] is a > > > > file-scope array, is the p4_ prefix even needed? > > > > > > I prefer them to be distinguished this way, since the .c file in > > > real is included into another (perf_event.c) file. > > > > That should probably be fixed btw. - but yeah, until the PMU drivers > > are separated out better the prefix is fine. > > I thought about adding some additional Kconfig where we would > choose which PMU to compile in, not sure though where is the best > place for it (under which menu section I mean). No need for any additional Kconfig for that, we could just build them as separate .o's. Thanks, Ingo