linux-kernel - Re: [RFC][PATCH] blktrace: fix original blktrace

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Date:	Wed, 25 Mar 2009 15:25:41 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Jens Axboe <jens.axboe@...cle.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] blktrace: fix original blktrace

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;

> back to block/blktrace.c, period.
> 
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