From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754373Ab0ELSXh (ORCPT ); Wed, 12 May 2010 14:23:37 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:48097 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753377Ab0ELSXg (ORCPT ); Wed, 12 May 2010 14:23:36 -0400 Date: Wed, 12 May 2010 20:23:21 +0200 From: Ingo Molnar To: Steven Rostedt Cc: Frederic Weisbecker , Pierre Tardy , Arnaldo Carvalho de Melo , Peter Zijlstra , Tom Zanussi , Paul Mackerras , linux-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com, arjan@infradead.org, ziga.mahkovec@gmail.com Subject: Re: [RFC] PyTimechart Message-ID: <20100512182321.GA10510@elte.hu> References: <20100511213625.GD5422@nowhere> <20100512144811.GA5405@nowhere> <1273678596.27703.30.camel@gandalf.stny.rr.com> <20100512165947.GA11921@elte.hu> <1273684511.27703.37.camel@gandalf.stny.rr.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1273684511.27703.37.camel@gandalf.stny.rr.com> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -1.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.0 required=5.9 tests=BAYES_20 autolearn=no SpamAssassin version=3.2.5 -1.0 BAYES_20 BODY: Bayesian spam probability is 5 to 20% [score: 0.1748] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Steven Rostedt wrote: > On Wed, 2010-05-12 at 18:59 +0200, Ingo Molnar wrote: > > * Steven Rostedt wrote: > > > > > On Wed, 2010-05-12 at 16:48 +0200, Frederic Weisbecker wrote: > > > > On Wed, May 12, 2010 at 03:37:27PM +0200, Pierre Tardy wrote: > > > > > > > But we don't yet support trace_printk in perf. May be we could wrap > > > > them in trace events. > > > > > > Hmm, do we really want to do that? > > > > > > We really need to get the perf and ftrace trace buffers combined. I > > > understand why perf chose to do the mmap buffers for the counting, but > > > for live streaming, it is very inefficient compared to splice. > > > > The thing is that for a very long time ftrace didnt have splice support > > and survived just fine. Even today most of the ftrace usage isnt utilizing > > splice. > > Actually, trace-cmd implements the splice interface and is used by several > people. I find myself using trace-cmd 90% of the time that I use ftrace, > specifically because of this speedup. i know, but most people still use /debug/tracing/ bits not trace-cmd. > > Yes, splice might help in some situations but on average it's an > > independent speedup on the order of magnitude of a few percents, not a > > 'must have' item. > > I'll have start running benchmarks to see what the actual speed up is. I'm > guessing it may be more than a few percent. It allows for zero copy overhead > and reuse of the data page. Make sure you measure it in the context of a full app like PyTimechart. You can measure the overhead using perf stat ;-) Ingo