aio_read template.

[Volker Lendecke]

On Wed, Jun 08, 2005 at 11:20:37AM +1000, James Peach wrote:
> Jeremy, do you have a specific workload where using aio would help?

The specific workload is an application reading multiple large data streams
simultaneously. The application itself reads sequentially, but the Win32 layer
of XPSP2 messes that up, so the Samba server sees nonsequential reads. The
Samba server has a cluster file system in the backend which depends on read
prediction that only hits when it sees sequential reads. With a pure unix
program for sequential reads I get about 350MB/sec out of this box, with the
pattern XPSP2 gives me it drops to about 60-80MB/sec, but sort of
varying. Feeding the kernel with the same pattern (multiple data streams) in
an AIO fashion I can bump that back to 140MB/sec. This is probably enough to
again saturate a gigabit link if you take the win32/smb/samba overhead into
account.

Volker
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