Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1032176Ab0B1WYX (ORCPT ); Sun, 28 Feb 2010 17:24:23 -0500 Received: from mail-ew0-f220.google.com ([209.85.219.220]:51790 "EHLO mail-ew0-f220.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1032129Ab0B1WYV (ORCPT ); Sun, 28 Feb 2010 17:24:21 -0500 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=nUExOgEpNKDC+Tv/eGHF9OecADo/FiFC/Hxi3kcyHh7FWeYyH1451bzBOqw4VgxC66 k/MisS+RN1H6fb9i44fD8/ANpIloFT1+i8/mXFaMpLMat/Kfs0uXZi6n7oUNh2lsqsA4 0FlSKEHNwVUM6v5NmgVCQyqs2DBWQDutyFKf8= Date: Sun, 28 Feb 2010 23:24:16 +0100 From: Frederic Weisbecker To: Peter Zijlstra Cc: Ingo Molnar , Lai Jiangshan , paulmck@linux.vnet.ibm.com, LKML , Arnaldo Carvalho de Melo , Steven Rostedt , Paul Mackerras , Hitoshi Mitake , Li Zefan , Masami Hiramatsu , Jens Axboe Subject: Re: [PATCH 10/11] tracing/perf: Fix lock events recursions in the fast path Message-ID: <20100228222412.GD5248@nowhere> References: <1265188475-23509-1-git-send-regression-fweisbec@gmail.com> <1265188475-23509-11-git-send-regression-fweisbec@gmail.com> <20100204154700.GE6676@linux.vnet.ibm.com> <4B6B84A1.60805@cn.fujitsu.com> <1265363102.22001.286.camel@laptop> <1265363441.22001.300.camel@laptop> <20100205104937.GB29515@elte.hu> <1265371808.22001.502.camel@laptop> <1265371973.22001.508.camel@laptop> <1265374915.22001.562.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1265374915.22001.562.camel@laptop> 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: 2349 Lines: 50 On Fri, Feb 05, 2010 at 02:01:55PM +0100, Peter Zijlstra wrote: > On Fri, 2010-02-05 at 13:12 +0100, Peter Zijlstra wrote: > > On Fri, 2010-02-05 at 13:10 +0100, Peter Zijlstra wrote: > > > On Fri, 2010-02-05 at 11:49 +0100, Ingo Molnar wrote: > > > > > > > > > That said, I'm not at all happy about removing lockdep annotations to make > > > > > the tracer faster, that's really counter productive. > > > > > > > > Are there no dynamic techniques that could be used here? > > > > > > > > Lockdep obviously wants maximum instrumentation coverage - performance be > > > > damned. > > > > > > > > Lock profiling/tracing/visualization wants the minimum subset of events it is > > > > interested in - everything else is unnecessary overhead. > > > > > > Well, they could start by moving the tracepoint inside the lockdep > > > recursion check. > > > > IIRC the reason its now outside is that you'd loose tracepoint on > > lockdep_off() usage, but having the tracer folks help on removing any > > such usage is of course a good thing. > > > > The usage thereof in nmi_enter() doesn't seem like a problem, since > > you're not supposed to be using locks from nmi context anyway, more so, > > I'd not be adverse to putting BUG_ON(in_nmi()) in every lockdep hook. > > Another nasty side effect is that it (lockdep recursion) isn't IRQ aware > in that we don't do any tracking for IRQ's that hit while we're doing > lockdep. We can fix that using a recursion context like we did for perf, > that would actually improve lockdep itself too. Actually, looking at lock_acquire/release/acquired/contended, they are all performing their job under a raw_lock_irq_save() window, so it doesn't seem we are losing anything. Something that could be nice though: dropping this irq saving from the main window, add the perf style recursion protection, and eventually have a raw_local_irq_save only when we take internal lockdep locks. This will let irqs happen during lockdep checks. I just guess the irq disabled thing is also protecting something else, something I'll probably discover after testing that :) -- 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/