linux-kernel - Re: blktrace: event traces displayed wrong while ftrace blktrace is active

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Message-ID: <20090415001617.GB8359@ghostprotocols.net>
Date:	Tue, 14 Apr 2009 21:16:17 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Theodore Tso <tytso@....edu>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: blktrace: event traces displayed wrong while ftrace blktrace
	is active

Em Tue, Apr 14, 2009 at 05:32:07PM -0400, Theodore Tso escreveu:
> On Tue, Apr 14, 2009 at 11:25:33PM +0200, Frederic Weisbecker wrote:
> > 
> > Indeed. Note that you can overwrite this default by typing:
> > 
> > echo context-info > trace_option
> > 
> > after setting bkltrace as the current tracer.
> 
> The problem with doing that is that blktrace will then display this:
> 
>     fsync-tester-27934 [001]   208.031278:     fsync-tester-27934 [001]   208.031278: 254,4    Q  WS 268392 + 8 [fsync-tester]
> 
> I think the real problem is that blk trace is displaying the standard
> context-info, so it's suppressing the normal context info.  So I have
> the choice on having no context information on my event trace lines,
> or two copies of the context information for the block trace lines.  
> 
> :-(
> 
> I'm guessing things were done this way in order to support the old
> legancy blktrace format?

Well, last time I worked in this code the default was to use the default
context information, not duplicate it, and if one used:

echo blk_classic > /sys/kernel/debug/tracing/trace_options

Then it would look like the output of blktrace(8).

Lemme try to boot the current code...

- Arnaldo
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