From: Theodore Ts'o <tytso@mit.edu>
Subject: Re: Excessive stall times on ext4 in 3.9-rc2
Date: Tue, 2 Apr 2013 14:19:40 -0400
Message-ID: <20130402181940.GA4936@thunk.org>
References: <20130402142717.GH32241@suse.de>
 <20130402150651.GB31577@thunk.org>
 <20130402151436.GC31577@thunk.org>
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To: Mel Gorman <mgorman@suse.de>, linux-ext4@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>,
	Jiri Slaby <jslaby@suse.cz>
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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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