From: Dave Chinner <dchinner@xxxxxxxxxx> I'd been trying to track down a behavioural difference between non-crc and crc enabled filesystems that was resulting non-crc filesystem executing prefetch almost 3x faster than CRC filesystems. After amny ratholes, I finally stumbled on the fact that btree format directories are not being prefetched due to a missing magic number check, and it's rejecting all XFS_BMAP_CRC_MAGIC format BMBT buffers. This makes prefetch on CRC enabled filesystems behave the same as for non-CRC filesystems. The difference a single line of code can make on a 50 million inode filesystem with a single threaded prefetch enabled run is pretty amazing. It goes from 3,000 iops @ 50MB/s to 2,000 IOPS @ 800MB/s and the cache hit rate goes from 3% to 49%. The runtime difference: Unpatched: Phase Start End Duration Phase 1: 02/21 18:34:12 02/21 18:34:12 Phase 2: 02/21 18:34:12 02/21 18:34:15 3 seconds Phase 3: 02/21 18:34:15 02/21 18:40:09 5 minutes, 54 seconds Phase 4: 02/21 18:40:09 02/21 18:46:36 6 minutes, 27 seconds Phase 5: 02/21 18:46:36 02/21 18:46:37 1 second Phase 6: 02/21 18:46:37 02/21 18:52:51 6 minutes, 14 seconds Phase 7: 02/21 18:52:51 02/21 18:52:52 1 second Total run time: 18 minutes, 40 seconds Patched: Phase Start End Duration Phase 1: 02/21 19:58:23 02/21 19:58:23 Phase 2: 02/21 19:58:23 02/21 19:58:27 4 seconds Phase 3: 02/21 19:58:27 02/21 19:59:20 53 seconds Phase 4: 02/21 19:59:20 02/21 20:00:07 47 seconds Phase 5: 02/21 20:00:07 02/21 20:00:08 1 second Phase 6: 02/21 20:00:08 02/21 20:00:50 42 seconds Phase 7: 02/21 20:00:50 02/21 20:00:50 Total run time: 2 minutes, 27 seconds Is no less impressive. Shame it's just a regression fix. ;) Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> --- repair/prefetch.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/repair/prefetch.c b/repair/prefetch.c index f4f3d71..946e822 100644 --- a/repair/prefetch.c +++ b/repair/prefetch.c @@ -298,7 +298,8 @@ pf_scanfunc_bmap( /* * do some validation on the block contents */ - if ((be32_to_cpu(block->bb_magic) != XFS_BMAP_MAGIC) || + if ((block->bb_magic != cpu_to_be32(XFS_BMAP_MAGIC) && + block->bb_magic != cpu_to_be32(XFS_BMAP_CRC_MAGIC)) || (be16_to_cpu(block->bb_level) != level)) return 0; -- 1.8.4.rc3 _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
