From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757039AbYKUUHn (ORCPT ); Fri, 21 Nov 2008 15:07:43 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754532AbYKUUHg (ORCPT ); Fri, 21 Nov 2008 15:07:36 -0500 Received: from mail-qy0-f11.google.com ([209.85.221.11]:33054 "EHLO mail-qy0-f11.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754119AbYKUUHf convert rfc822-to-8bit (ORCPT ); Fri, 21 Nov 2008 15:07:35 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references; b=h5JpeP3K4sr46wT+/DS/yU4XIHC1T8rV8Uytx6KErb2huWw/K/B2uRTOlNjh14upF6 6Fn8TVlhzfuVqKNHMAhklvtDU73DTo58ZKPfm652J06BqJhCGISpCioWB9aEREalHsQi F1FHv6tgoDDFTqTT05pgqnCQUI6+c9ys2onCA= Message-ID: Date: Fri, 21 Nov 2008 21:07:33 +0100 From: "=?ISO-8859-1?Q?Fr=E9d=E9ric_Weisbecker?=" To: "Ingo Molnar" Subject: Re: [PATCH 3/3] tracing/function-return-tracer: add the overrun field Cc: "Steven Rostedt" , "Linux Kernel" In-Reply-To: <20081121194819.GA568@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Content-Disposition: inline References: <20081118145154.GC30358@elte.hu> <20081118151326.GH30358@elte.hu> <20081118155045.GJ30358@elte.hu> <20081118164019.GA18620@elte.hu> <20081118210344.GC11490@elte.hu> <20081121194819.GA568@elte.hu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2008/11/21 Ingo Molnar : > > * 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 > Ok. I thought about this method but wondered about the fact that kmalloc can schedule and then I could run in an infinite loop (or a too long one). I will try this. Thanks.