concurrent direct IO write in xfs

[Christoph Hellwig]

On Sun, Jan 15, 2012 at 07:01:42PM -0500, Zheng Da wrote:
> Hello,
> 
> I surprisedly found that writing data to a file (no appending) with direct
> IO and with multiple threads has the same performance as a single thread.
> Actually, it seems there is only one core is working at a time. In my case,
> each time I write a page to a file and the offset is always aligned to the
> page size, so there is no overlapping between writes.

What kernel version are you using?  Also, what is the exact I/O
pattern?