From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758218AbZCYNBt (ORCPT ); Wed, 25 Mar 2009 09:01:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752665AbZCYNBl (ORCPT ); Wed, 25 Mar 2009 09:01:41 -0400 Received: from brick.kernel.dk ([93.163.65.50]:46294 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752501AbZCYNBl (ORCPT ); Wed, 25 Mar 2009 09:01:41 -0400 Date: Wed, 25 Mar 2009 14:01:39 +0100 From: Jens Axboe To: Ingo Molnar Cc: Li Zefan , Arnaldo Carvalho de Melo , Frederic Weisbecker , Steven Rostedt , LKML Subject: Re: [RFC][PATCH] blktrace: fix original blktrace Message-ID: <20090325130138.GO27476@kernel.dk> References: <49C99BD2.9090503@cn.fujitsu.com> <20090325070726.GD27476@kernel.dk> <49C9DC75.9080301@cn.fujitsu.com> <20090325072704.GF27476@kernel.dk> <20090325125231.GE30755@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090325125231.GE30755@elte.hu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 25 2009, Ingo Molnar wrote: > > * Jens Axboe wrote: > > > On Wed, Mar 25 2009, Li Zefan wrote: > > > Jens Axboe wrote: > > > > On Wed, Mar 25 2009, Li Zefan wrote: > > > >> I'm wondering what we are going to do with the original blktrace which > > > >> is using relay and is used via ioctl. > > > >> > > > >> The problem is currently it's totally broken. You can use ftrace to see > > > >> the output of blktrace, but user-space blktrace is unusable. > > > >> > > > >> With this patch, both ioctl and ftrace can be used, but of course you > > > >> can't use both of them at the same time. > > > > > > > > Even if ftrace was as fast as storing huge amounts of data as blktrace, > > > > it's still of utmost importance that nothing is broken there. There are > > > > > > agreed > > > > > > > people actually USING this tracing to do real work, it's not a > > > > playground. > > > > > > > > > > and we are using blktrace to test the cgroup-based io controller > > > > > > > I appreciate the efforts to unify and improve our tracing, but we must > > > > not be breaking blktrace along the way. Otherwise the whole thing goes > > > > > > this patch fixes it. > > > > > > it's broken by "blktrace: add ftrace plugin" > > > (c71a896154119f4ca9e89d6078f5f63ad60ef199) > > > > > > @@ -131,13 +162,14 @@ static void __blk_add_trace() > > > - if (unlikely(bt->trace_state != Blktrace_running)) > > > + if (unlikely(bt->trace_state != Blktrace_running || !blk_tracer_enabled)) > > > return; > > > > Good, as long as it still works with blktrace, that's all I care > > about (for now, at least). > > Sorry about that. I've applied Li's fixes and double checked > blktrace+blktrace functionality and pushed out a new tracing > tree to linux-next. > > Btw., blktrace could be updated in the future to make use the > new per CPU buffering and sys_splice() code available in ftrace > plugin. [ splice is cool! =B-) ] > > Plus blktrace could make use of built-in event filtering > capabilities - for example to only trace events in a specific > sector range on the disk. Or to trace all IO of a given PID only. > > But that is a different project that needs changes both on the > kernel side and on the user-space side (.31-ish for sure) and the > relayfs+ioctl method must work fine in any case. Don't get me wrong, I completely agree with the unification idea, it'll be awesome to have a single stream of info for several event types. My worry was just if it was going too fast, I just don't want a broken blktrace before the dust has even settled. And moving blktrace from relay to per-cpu buffering and splice definitely sounds like a good longer term direction. -- Jens Axboe