Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755900Ab0BEMNZ (ORCPT ); Fri, 5 Feb 2010 07:13:25 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:36977 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755262Ab0BEMNY (ORCPT ); Fri, 5 Feb 2010 07:13:24 -0500 Subject: Re: [PATCH 10/11] tracing/perf: Fix lock events recursions in the fast path From: Peter Zijlstra To: Ingo Molnar Cc: Lai Jiangshan , paulmck@linux.vnet.ibm.com, Frederic Weisbecker , LKML , Arnaldo Carvalho de Melo , Steven Rostedt , Paul Mackerras , Hitoshi Mitake , Li Zefan , Masami Hiramatsu , Jens Axboe In-Reply-To: <1265371808.22001.502.camel@laptop> 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> Content-Type: text/plain; charset="UTF-8" Date: Fri, 05 Feb 2010 13:12:53 +0100 Message-ID: <1265371973.22001.508.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1293 Lines: 30 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. -- 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/