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

[Mike Galbraith]

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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