On Tue, Apr 12, 2011 at 10:58:53AM +0300, Raz wrote: > Christoph Hello > I am testing 2.6.38 with AIM benchmark. > I compared 2.6.38 to 2.6.27 and I noticed that 2.6.27 is much better > than 2.6.38 when > doing sync random writes test over an xfs regular file over native > Linux partition on top common sata disk. > I git bisected the problem and I reached this SHA1: > commit 13e6d5cdde0e785aa943810f08b801cadd0935df > Author: Christoph Hellwig <hch@xxxxxx> > Date: Mon Aug 31 21:00:31 2009 -0300 > > xfs: merge fsync and O_SYNC handling > > The guarantees for O_SYNC are exactly the same as the ones we need to > make for an fsync call (and given that Linux O_SYNC is O_DSYNC the > equivalent is fdadatasync, but we treat both the same in XFS), except > with a range data writeout. Jan Kara has started unifying these two > path for filesystems using the generic helpers, and I've started to > look at XFS. > ... > > > The bellow two tests presents the how different performance is before and patch: > #test 16) bisect 11 > ------------------------------------------------------------------------------------------------------------ > Test Test Elapsed Iteration Iteration Operation > Number Name Time (sec) Count Rate (loops/sec) Rate (ops/sec) > ------------------------------------------------------------------------------------------------------------ > 1 sync_disk_rw 30.71 19 0.61869 1583.85 > Sync Random Disk Writes (K)/second > ------------------------------------------------------------------------------------------------------------ That's clearly showing that your sync writes are not hitting the disk. IOWs, the sync writes are not synchronous at all. There is no way a single SATA drive can do >1500 writes to stable storage per second. IOWs, before this fix, sync writes were broken on your hardware. > #test 17 ) bisect 12 > ------------------------------------------------------------------------------------------------------------ > 1 sync_disk_rw 69.05 1 0.01448 37.07 > Sync Random Disk Writes (K)/second > ------------------------------------------------------------------------------------------------------------ And that's pretty tpyical for a SATA drive where sync writes are actually hitting the platter correctly. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
