Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754566AbZCTIcV (ORCPT ); Fri, 20 Mar 2009 04:32:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753251AbZCTIbw (ORCPT ); Fri, 20 Mar 2009 04:31:52 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:34345 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754923AbZCTIbt (ORCPT ); Fri, 20 Mar 2009 04:31:49 -0400 Date: Fri, 20 Mar 2009 09:30:49 +0100 From: Ingo Molnar To: Miklos Szeredi Cc: peterz@infradead.org, roland@redhat.com, efault@gmx.de, rjw@sisk.pl, jdike@addtoit.com, user-mode-linux-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: [patch] fix uml slowness caused by ptrace preemption bug on host Message-ID: <20090320083049.GA29471@elte.hu> References: <1237537169.24626.29.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian 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 Content-Length: 1304 Lines: 37 * Miklos Szeredi wrote: > On Fri, 20 Mar 2009, Peter Zijlstra wrote: > > On Thu, 2009-03-19 at 23:23 +0100, Miklos Szeredi wrote: > > > > > > This patch solves this by not scheduling on preempt_enable() after > > > ptrace_stop() has woken up the tracer. > > > > Nice,.. however did you find this? > > Ftrace helped a lot, it's a really cool tool :). I had to patch it > with this, otherwise the timestamps would be totally off: > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index bd38c5c..557c2dd 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -108,7 +108,7 @@ u64 ring_buffer_time_stamp(int cpu) > > preempt_disable_notrace(); > /* shift to debug/test normalization and TIME_EXTENTS */ > - time = sched_clock() << DEBUG_SHIFT; > + time = cpu_clock(cpu) << DEBUG_SHIFT; > preempt_enable_no_resched_notrace(); Btw., based on your earlier report, the same is now possible in the latest tracing tree via: echo 1 > /debug/tracing/options/global_clock Ingo -- 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/