linux-kernel - Re: 3.4.4-rt13: btrfs + xfstests 006 = BOOM.. and a bonus rt_mutex deadlock report for absolutely free!

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Date:	Sat, 14 Jul 2012 15:38:16 +0200
From:	Mike Galbraith <efault@....de>
To:	Chris Mason <chris.mason@...ionio.com>
Cc:	"linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: 3.4.4-rt13: btrfs + xfstests 006 = BOOM..  and a bonus rt_mutex
 deadlock report for absolutely free!

On Fri, 2012-07-13 at 08:50 -0400, Chris Mason wrote:

> There is also a chunk of code in btrfs_clear_path_blocking that makes
> sure to strictly honor top down locking order during the conversion.  It
> only does this when lockdep is enabled because in non-RT kernels we
> don't need to worry about it.  For RT we'll want to enable that as well.

Hm, _seems_ that alone is enough prevent deadlock.  Throughput really
sucks though.  The other bits of my stab bump throughput for dbench 128
from ~200 mb/s to ~360 mb/s (appears it's the paranoid trylock loops).
ext3 does 775 mb/s with the same kernel.  Or, dbench 8 on ext3 gives
~1800 mb/s and ~480 mb/s btrfs.  Not exactly wonderful.

Hohum, guess I'll wait and see what your patch looks like.  I bet it'll
work a lot better than mine does :)

-Mike

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