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

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Message-ID: <20130408105253.GA5275@redhat.com>
Date:	Mon, 8 Apr 2013 06:52:53 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	"Theodore Ts'o" <tytso@....edu>, 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

Hi, Mel -

> > [...]  git kernel developers
> > should use git systemtap, as has always been the case.  [...]
> 
> At one point in the past this used to be the case but then systemtap had to
> be compiled as part of automated tests across different kernel versions. It
> could have been worked around in various ways or even installed manually
> when machines were deployed but stap-fix.sh generally took less time to
> keep working.

OK, if that works for you.  Keep in mind though that newer versions of
systemtap retain backward-compatibility for ancient versions of the
kernel, so git systemtap should work on those older versions just
fine.


> [...]
> Yes, this was indeed the problem. The next version of watch-dstate.pl
> treated get_request_wait() as a function that may or may not exist. It
> uses /proc/kallsyms to figure it out.

... or you can use the "?" punctuation in the script to have
systemtap adapt:

    probe kprobe.function("get_request_wait") ?  { ... }


- FChE
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