From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753442Ab0CQHbA (ORCPT ); Wed, 17 Mar 2010 03:31:00 -0400 Received: from ns.dcl.info.waseda.ac.jp ([133.9.216.194]:51473 "EHLO ns.dcl.info.waseda.ac.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752579Ab0CQHa7 (ORCPT ); Wed, 17 Mar 2010 03:30:59 -0400 Message-ID: <4BA0852D.1090300@dcl.info.waseda.ac.jp> Date: Wed, 17 Mar 2010 16:30:53 +0900 From: Hitoshi Mitake User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.5) Gecko/20091211 Shredder/3.0 MIME-Version: 1.0 To: Frederic Weisbecker CC: Peter Zijlstra , linux-kernel@vger.kernel.org, h.mitake@gmail.com, Ingo Molnar , Paul Mackerras , Arnaldo Carvalho de Melo , Jens Axboe , Jason Baron Subject: Re: [PATCH RFC 00/11] lock monitor: Separate features related to lock References: <1268563128-6486-1-git-send-email-mitake@dcl.info.waseda.ac.jp> <1268590435.9440.8.camel@laptop> <20100317013236.GB5258@nowhere> In-Reply-To: <20100317013236.GB5258@nowhere> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/17/10 10:32, Frederic Weisbecker wrote: > On Sun, Mar 14, 2010 at 07:13:55PM +0100, Peter Zijlstra wrote: >> On Sun, 2010-03-14 at 19:38 +0900, Hitoshi Mitake wrote: >>> Current lockdep is too complicated because, >>> * dependency validation >>> * statistics >>> * event tracing >>> are all implemented by it. >>> This cause problem of overhead. >>> If user enables one of them, overhead of rests part is not avoidable. >>> (tracing is exception. If user enables validation or stat, >>> overhead of tracing doesn't occur.) >>> >>> So I suggest new subsystem "lock monitor". >>> This is a general purpose lock event hooking mechanism. >>> >>> lock monitor will be enable easy implementing and running >>> these features related to lock. >>> >>> And I'm hoping that lock monitor will reduce overhead of perf lock. >>> Because lock monitor separates dependency validation and event tracing clearly, >>> so calling of functions of lockdep (e.g. lock_acquire()) only for validation >>> will not occur lock events. >>> >>> I implemented it on the branch perf/inject of Frederic's random-tracing tree. >>> Because the branch is hottest place of lock and tracing :) >> >> OK, so I really don't like this much.. >> >> Building a lockstat kernel (PROVE_LOCKING=n) should not have much more >> overhead than the proposed solution, if the simple lock acquistion >> tracking bothers you, you can do a patch to weaken that. >> >> I really really dislike how you add a monitor variable between >> everything for no reason what so ever. >> >> You use a new rwlock_t, which is an instant fail, those things are worse >> than useless. >> >> You add chained indirect calls into all lock ops, that's got to hurt. > > > Well, the idea was not bad at the first glance. It was separating > lockdep and lock events codes. > > But indeed, the indirect calls plus the locking are not good > for such a fast path. > > There is something else, it would be nice to keep the > lockdep_map -> lockdep_class mapping so that we can > do lock profiling based on classes too. So we actually > need the lockdep code. What we don't need is the prove > locking or the lock stats. So I guess we can have a new > config to enable lock events and get rid of the prove > locking / lock stat code if we don't need it. > > Thanks for your comments, Peter and Frederic. My main motivation of writing this patch series was that some kernel codes uses lockdep functions (e.g. lock_acquire()) directly, so perf lock gets a lot of trace events without actual locks (e.g. might_lock_read()). I think that these are confusable things for users. But I noticed that these events can be reduced by turning off CONFIG_PROVE_LOCKING. Yeah, my patch series was pointless... :) Should perf lock warn not to use with CONFIG_PROVE_LOCKING? Thanks, Hitoshi