From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <466993CF.4050804@de.ibm.com> Date: Fri, 08 Jun 2007 19:37:19 +0200 From: Martin Peschke MIME-Version: 1.0 Subject: Re: [RFC] [Patch 4/4] lock contention tracking slimmed down References: <1181165656.7133.23.camel@dix> <1181202258.7348.217.camel@twins> <46698B1D.3000806@de.ibm.com> <1181322460.5728.2.camel@lappy> <46698F7F.4090407@de.ibm.com> <1181323622.5728.6.camel@lappy> In-Reply-To: <1181323622.5728.6.camel@lappy> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, jbaron@redhat.com, rostedt@goodmis.org, billh@gnuppy.monkey.org, mingo@elte.hu, linux-s390@vger.kernel.org List-ID: Peter Zijlstra wrote: > On Fri, 2007-06-08 at 19:18 +0200, Martin Peschke wrote: >> Peter Zijlstra wrote: >>> On Fri, 2007-06-08 at 19:00 +0200, Martin Peschke wrote: >>>> Peter Zijlstra wrote: >>>>> I'm confused as to where the class->stat objects are initialised? Is >>>>> that done in lock_stat_init()? If so, then you have a bug. >>>> static struct lock_class lock_classes[MAX_LOCKDEP_KEYS]; >>>> >>>> I assume this gets us class structures containing all zeros, doesn't it? >>>> Then class->stat is zeros as well, which is handled by lib/statistics. >>>> (In this case, data gathering hasn't been turned on yet, and statistic_inc() >>>> and similar functions don't access other areas of struct statistic.) >>> Who eventually calls percpu_alloc? >> There is a small state machine calling percpu_alloc when users do >> >> echo state=on > /debug/statistics/lockdep/definition >> >> So data gathering is off by default. >> >> It might make sense to allow "state=on" as a default. Then allocation would >> be done in the context of statistic_attach(). > > Right, the problem here is that you iterate over all_lock_classes once > at init. > > Contrary to what the name might suggest, it are not all possible > classes, just all active ones. So you'll only attach the classes which > have been used up until the init point. All other classes used later > will never be initialized. Ah.. Do you know where a class is setup for first use? I guess it is feasible to move statistic initialisation to that place. Is there a place where a class becomes unused again?