From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756365AbYKUTsk (ORCPT ); Fri, 21 Nov 2008 14:48:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756234AbYKUTsb (ORCPT ); Fri, 21 Nov 2008 14:48:31 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:49289 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755242AbYKUTsa (ORCPT ); Fri, 21 Nov 2008 14:48:30 -0500 Date: Fri, 21 Nov 2008 20:48:19 +0100 From: Ingo Molnar To: =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker Cc: Steven Rostedt , Linux Kernel Subject: Re: [PATCH 3/3] tracing/function-return-tracer: add the overrun field Message-ID: <20081121194819.GA568@elte.hu> References: <20081118145154.GC30358@elte.hu> <20081118151326.GH30358@elte.hu> <20081118155045.GJ30358@elte.hu> <20081118164019.GA18620@elte.hu> <20081118210344.GC11490@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit 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=3.2.3 -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 * Frédéric Weisbecker wrote: > When the tracer will be launched, I will hold the tasklist_lock to > allocate/insert the dynamic arrays. So in this atomic context, I > will not be able to call kmalloc with GFP_KERNEL. And I fear that > using GFP_ATOMIC for possible hundreds of tasks would be clearly > unacceptable. > > What do you think of this way: > > _tracer activates > _a function enters the tracer entry-hooker. If the array is allocated > for the current task, that's well. If not I launch a kernel thread > that will later allocate an array for the current task (I will pass > the pid as a parameter). So the current task will be soon be traced. > _ when a process forks, I can allocate a dynamic array for the new > task without problem (I hope). > > So some tasks will not be traced at the early beggining of tracing > but they will soon all be traced.... There is perhaps a problem with > tasks that are sleeping for long times... There will be some losses > once they will be awaken... i'd suggest a different approach that is simpler: - step0: set flag that "all newly created tasks need the array allocated from now on". - step1: allocate N arrays outside tasklist_lock - step2: take tasklist_lock, loop over all tasks that exist and pass in the N arrays to all tasks that still need it. If tasks were 'refilled', drop tasklist_lock and go back to step 1. - step3: free N (superfluously allocated) arrays Make N something like 32 to not get into a bad quadratic nr_tasks double loop in practice. (Possibly allocate arrays[32] dynamically as well at step0 and not have it on the kernel stack - so 32 can be changed to 128 or so.) Ingo