From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755303AbZCEHab (ORCPT ); Thu, 5 Mar 2009 02:30:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753321AbZCEHaW (ORCPT ); Thu, 5 Mar 2009 02:30:22 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:40710 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753096AbZCEHaW (ORCPT ); Thu, 5 Mar 2009 02:30:22 -0500 Subject: Re: [PATCH 2/2] tracing/function-graph-tracer: use the more lightweight local clock From: Peter Zijlstra To: Frederic Weisbecker Cc: Ingo Molnar , Steven Rostedt , linux-kernel@vger.kernel.org In-Reply-To: <20090305011941.GA9821@nowhere> References: <49af243d.06e9300a.53ad.ffff840c@mx.google.com> <20090305011941.GA9821@nowhere> Content-Type: text/plain Date: Thu, 05 Mar 2009 08:30:13 +0100 Message-Id: <1236238213.5330.10111.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.25.91 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2009-03-05 at 02:19 +0100, Frederic Weisbecker wrote: > It takes 1 ms to execute while tracing. > Considering my frequency is 250 Hz, it means 1/4 of the system is used > on timer interrupt while tracing. > > For now the hang is fixed, but not the awful latency. And I'm just too frightened > to test it on 1000 Hz. > > But I plan to add a kind of watchdog to check how many time we spent inside an > interrupt while graph tracing. > By checking this time against the current Hz value, I could decide to abort the tracing > for all irq. That would basically render the thing useless :-( Is it specifically function_graph that is so expensive? If so, is that because of the function exit hook?