linux-kernel - Re: Excessive stall times on ext4 in 3.9-rc2

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Date:	Tue, 2 Apr 2013 14:19:40 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Mel Gorman <mgorman@...e.de>, linux-ext4@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>, Jiri Slaby <jslaby@...e.cz>
Subject: Re: Excessive stall times on ext4 in 3.9-rc2

So I tried to reproduce the problem, and so I installed systemtap
(bleeding edge, since otherwise it won't work with development
kernel), and then rebuilt a kernel with all of the necessary CONFIG
options enabled:

	CONFIG_DEBUG_INFO, CONFIG_KPROBES, CONFIG_RELAY, CONFIG_DEBUG_FS,
	CONFIG_MODULES, CONFIG_MODULE_UNLOAD

I then pulled down mmtests, and tried running watch-dstate.pl, which
is what I sasume you were using, and I got a reminder of why I've
tried very hard to use systemtap:

semantic error: while resolving probe point: identifier 'kprobe' at /tmp/stapdjN4_l:18:7
        source: probe kprobe.function("get_request_wait")
                      ^

semantic error: no match
semantic error: while resolving probe point: identifier 'kprobe' at :74:8
        source: }probe kprobe.function("get_request_wait").return
                       ^

Pass 2: analysis failed.  [man error::pass2]
Unexpected exit of STAP script at ./watch-dstate.pl line 296.

I have no clue what to do next.  Can you give me a hint?

Thanks,

						- Ted
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