linux-kernel - Re: Is it a workqueue related issue in 2.6.37 (Was: Re: [libvirt] blkio cgroup [solved])

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Date:	Fri, 25 Feb 2011 21:47:40 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Dominik Klein <dk@...telegence.net>, Tejun Heo <tj@...nel.org>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	libvir-list@...hat.com
Subject: Re: Is it a workqueue related issue in 2.6.37 (Was: Re: [libvirt]
 blkio cgroup [solved])

On Fri, 2011-02-25 at 15:18 -0500, Vivek Goyal wrote:

> Thanks Steve. In this case this feature of sending trace data over
> network would have helped. We were running into issues where IO scheduler
> was freezing so we could not read anything from disk(including saved traces).
> Hence we were directing everything to console and then doing copy paste.
> 
> So sending it over network would have probably worked even in this case.
> 
> Will give trace-cmd a try next time.

Hi Vivek,

I just pushed out a hack that lets trace-cmd read the blktrace.

I found that the blktrace never exported its structure to
the /debug/tracing/events/ftrace/blktrace/format. So userspace has no
real way to know how to parse it.

Instead, I wrote a hack that creates this file semi dynamically, based
on the information of other events. I also copied a lot of the blktrace
code from the kernel so that it can print out the same format.

You need to install the plugin that is built with trace-cmd. It will
either be automatically installed if you do a make install, but if you
do not have root access, just cp the plugin_blk.so into
~/.trace-cmd/plugins directory (you may need to make that directory
yourself).  Then when you run trace-cmd report on a file made with the
blk tracer, it will give you a nice output.

If you already have a trace.dat file from a previous extract, you don't
need to run the trace again. The trace-cmd report will work on that file
now.

I'll be heading out to NYC on Monday for the End Users Conf and this
weekend I need to get all my chores done around the house for the misses
to let me go ;)  Thus, I wont be doing much more till I get back at the
end of next week.

-- Steve

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