On Fri, Jun 29, 2012 at 12:25:06PM +0100, Mel Gorman wrote:

Configuration:	global-dhp__io-metadata-xfs
Benchmarks:	dbench3, fsmark-single, fsmark-threaded

Summary
=======
Most of the figures look good and in general there has been consistent good
performance from XFS. However, fsmark-single is showing a severe performance
dip in a few cases somewhere between 3.1 and 3.4. fs-mark running a single
thread took a particularly bad dive in 3.4 for two machines that is worth
examining closer.

That will be caused by the fact we changed all the metadata updates
to be logged, which means a transaction every time .dirty_inode is
called.

This should mostly go away when XFS is converted to use .update_time
rather than .dirty_inode to only issue transactions when the VFS
updates the atime rather than every .dirty_inode call...

Unfortunately it is harder to easy conclusions as the
gains/losses are not consistent between machines which may be related to
the available number of CPU threads.

It increases the CPU overhead (dirty_inode can be called up to 4
times per write(2) call, IIRC), so with limited numbers of
threads/limited CPU power it will result in lower performance. Where
you have lots of CPU power, there will be little difference in
performance...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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