From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757371AbZEVKIZ (ORCPT ); Fri, 22 May 2009 06:08:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751791AbZEVKIR (ORCPT ); Fri, 22 May 2009 06:08:17 -0400 Received: from viefep12-int.chello.at ([62.179.121.32]:6777 "EHLO viefep12-int.chello.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751475AbZEVKIR (ORCPT ); Fri, 22 May 2009 06:08:17 -0400 X-SourceIP: 213.93.53.227 Subject: Re: [PATCH 2/2] perf_counter: optimize context switch between identical inherited contexts From: Peter Zijlstra To: Paul Mackerras Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Corey Ashford , Thomas Gleixner In-Reply-To: <18966.30400.611789.434936@cargo.ozlabs.ibm.com> References: <18966.10075.781053.231153@cargo.ozlabs.ibm.com> <18966.10666.517218.332164@cargo.ozlabs.ibm.com> <1242980169.26820.617.camel@twins> <18966.30400.611789.434936@cargo.ozlabs.ibm.com> Content-Type: text/plain Date: Fri, 22 May 2009 12:08:17 +0200 Message-Id: <1242986897.26820.638.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2009-05-22 at 19:56 +1000, Paul Mackerras wrote: > Peter Zijlstra writes: > > > On Fri, 2009-05-22 at 14:27 +1000, Paul Mackerras wrote: > > > Since we don't have individual fds for the counters in a cloned > > > context, the only thing that can make two clones of a given parent > > > different after they have been cloned is enabling or disabling all > > > counters with prctl. To account for this, we keep a count of the > > > number of enabled counters in each context. Two contexts must have > > > the same number of enabled counters to be considered equivalent. > > > > Curious point that.. so prctl() can disable counters it doesn't own. > > > > Shouldn't we instead fix that? > > Well, prctl enables/disables the counters that are counting on the > current process, regardless of who or what created them. I always > thought that was a little strange; maybe it is useful to be able to > disable all the counters that any other process might have put on to > you, but I can't think of a scenario where you'd really need to do > that, particularly since the disable is a one-shot operation, and > doesn't prevent new (enabled) counters being attached to you. > > On the other hand, what does "all the counters I own" mean? Does it > mean all the ones that I have fds open for? Or does it mean all the > ones that I created? Either way we don't have a good way to enumerate > them. I'm for all counters you created (ie have a fd for). Being able to disable counters others created on you just sounds wrong. If we can settle on a semantic, I'm sure we can implement it :-) Ingo, Corey, any opinions?