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Date: Wed, 25 Mar 2009 08:27:04 +0100
From: Jens Axboe <jens.axboe@oracle.com>
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: Ingo Molnar <mingo@elte.hu>, Arnaldo Carvalho de Melo <acme@redhat.com>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       Steven Rostedt <rostedt@goodmis.org>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC][PATCH] blktrace: fix original blktrace
Message-ID: <20090325072704.GF27476@kernel.dk>
References: <49C99BD2.9090503@cn.fujitsu.com> <20090325070726.GD27476@kernel.dk> <49C9DC75.9080301@cn.fujitsu.com>
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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).

-- 
Jens Axboe