From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755251AbYLTBij (ORCPT ); Fri, 19 Dec 2008 20:38:39 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752637AbYLTBib (ORCPT ); Fri, 19 Dec 2008 20:38:31 -0500 Received: from nf-out-0910.google.com ([64.233.182.189]:34597 "EHLO nf-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752355AbYLTBia (ORCPT ); Fri, 19 Dec 2008 20:38:30 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=sender:date:from:to:cc:subject:message-id:in-reply-to:references :x-mailer:mime-version:content-type:content-transfer-encoding; b=vmQfzh+OMTlz9W2eyDzbBYrpD/vU18GWiVhOx/bwYY+ZLLZlQ0CFi8Pppqhe8gRBxU yUWdSdQtVu8p3KWeimIJIBfh4Qu9na7xbDTBQOOL20v7gThRf36f6A44WmFt+Sx89iIK TWhfYjdEmu7CyHZ9AcpaMOCMlYIZ0caZ3NFRg= Date: Sat, 20 Dec 2008 03:38:22 +0200 From: Pekka Paalanen To: Steven Rostedt Cc: Ingo Molnar , =?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , Pekka J Enberg , LKML , Markus Metzger Subject: Re: ftrace behaviour (was: [PATCH] ftrace: introduce tracing_reset_online_cpus() helper) Message-ID: <20081220033822.362bc88a@daedalus.pq.iki.fi> In-Reply-To: References: <20081220004453.50aec846@daedalus.pq.iki.fi> <20081219225717.GK13409@elte.hu> <20081219233443.GC17984@elte.hu> X-Mailer: Claws Mail 3.6.1 (GTK+ 2.12.11; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 19 Dec 2008 19:29:30 -0500 (EST) Steven Rostedt wrote: > On Sat, 20 Dec 2008, Ingo Molnar wrote: > > > > The current "only allow resizing while tracing is disabled" is an > > unintuitive and counterproductive restriction - a borderline bug in fact. > > Having to disable tracing to resize is much better than having to reboot. > > I'm not defending that this is the way to go. I never planned on keeping > this the defacto standard. I've been setting up infrastructure to allow > for a seamless resize. If you think we should reset the buffers on resize, > then that would be a great way for the user to know why they are missing > **all** their data. I thought this was just about not having to do $ echo 0 > tracing_enabled $ echo 28764243 > buffer_size $ echo 1 > tracing_enabled and instead just do $ echo 28764243 > buffer_size which would do exactly the same, except being easier for the user. Personally I've never dreamed of any kind of resize-in-flight. > What I'm trying to say is that the more we allow during resize, the more > likely there will be a critical bug that might lock up the system. The > whole point about writing the ring buffer was to do it incrementally. > Start out with being straight forward and simple, then we could add > features as we understand things better. > > IOW, I totally agree that we should make it as intuitive as possible. But > this needs to be done step by step. I wrote 10 different versions of the > ring buffer in a week. Most of them were complete rewrites. I want this to > be as robust and powerful as you do, but I also want to be cautious about > doing things that might crash the system. > > Ftrace already had the infrastructure in place to protect against resize. > I just used it to give me time to do other things with the ring buffer. > I always planned on having the resize protection back inside the ring > buffer code when I got around to it. > > -- Steve -- Pekka Paalanen http://www.iki.fi/pq/