Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755131AbZG2AgQ (ORCPT ); Tue, 28 Jul 2009 20:36:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754950AbZG2AgQ (ORCPT ); Tue, 28 Jul 2009 20:36:16 -0400 Received: from mail-ew0-f226.google.com ([209.85.219.226]:34495 "EHLO mail-ew0-f226.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754271AbZG2AgP (ORCPT ); Tue, 28 Jul 2009 20:36:15 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=AT0scAI5T3I7WZ7nF6xpAOTti1HDD7/KdbNxZhpjVeqNI1Sr6fo91fqJ5kXWKpP5Ni bHfp/xWjQRKuWDYVQbX4xZFIbwKMniB9pM7+e97/VxPwiurIGWxxlcCQ4hvr7aAgH9Iv hEbZLc9BcR8Hq+uBQOVWhe0BimslbksFvYFfE= Date: Wed, 29 Jul 2009 02:36:09 +0200 From: Frederic Weisbecker To: Peter Zijlstra Cc: prasad@linux.vnet.ibm.com, Ingo Molnar , LKML , Steven Rostedt , Thomas Gleixner , Mike Galbraith , Paul Mackerras , Arnaldo Carvalho de Melo , Lai Jiangshan , Anton Blanchard , Li Zefan , Zhaolei , KOSAKI Motohiro , Mathieu Desnoyers , Alan Stern Subject: Re: [RFC][PATCH 5/5] perfcounter: Add support for kernel hardware breakpoints Message-ID: <20090729003607.GC5104@nowhere> References: <1248445569.6987.74.camel@twins> <20090724174723.GA11985@nowhere> <1248519416.5780.12.camel@laptop> <20090725141918.GA5295@nowhere> <1248538972.5780.25.camel@laptop> <20090725235702.GA5082@in.ibm.com> <1248684817.6987.1573.camel@twins> <20090728010349.GB5147@nowhere> <1248765877.6987.2754.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1248765877.6987.2754.camel@twins> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1303 Lines: 29 On Tue, Jul 28, 2009 at 09:24:37AM +0200, Peter Zijlstra wrote: > On Tue, 2009-07-28 at 03:03 +0200, Frederic Weisbecker wrote: > > > Thirdly, we can multiplex perf counters beyond their hardware maximum, > > > something you simply cannot do for a debug interface. > > > > > > Again, I'm stuck in what you mean by multiplexing here :-) > > If you'd create say 16 breakpoint counters, we'd RR them over the 4 > available hardware breakpoints (or less when others are taken by someone > else). > > Since its all statistics anyway, we can simply scale the event counts up > by the time-share they received. > Aah, ok I understand now. But I fear it may kill the accuracy of the breakpoints statistics. It's fine for a theoretical linear rate of breakpoint events. But what happens if we are profiling something much more unstable with a rain of hits in a small window of memory between large timeframes? If we have a breakpoint inside this window of memory and this breakpoint is not plugged, waiting for its turn in the RR, we loose this rain of events. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/