[PATCH] xfs_repair: multithread phase 2

[Alex Elder]

On Mon, 2011-01-10 at 11:44 +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner at redhat.com>
> 
> Running some recent repair tests on broken filesystem meant running
> phase 1 and 2 repeatedly to reproduce an issue at the start of phase
> 3. Phase 2 was taking approximately 10 minutes to run as it
> processes each AG serially.
> 
> Phase 2 can be trivially parallelised - it is simply scanning the
> per AG trees to calculate free block counts and free and used inodes
> counts. This can be done safely in parallel by giving each AG it's
> own structure to aggregate counts into, then once the AG scan is
> complete adding them all together.
> 
> This patch uses 32-way threading which results in no noticable
> slowdown on single SATA drives with NCQ, but results in ~10x
> reduction in runtime on a 12 disk RAID-0 array.
> 
> Signed-off-by: Dave Chinner <dchinner at redhat.com>

This looks good.  Sorry I didn't say so earlier (I signed
off on your first one).

Reviewed-by: Alex Elder <aelder at sgi.com>