Strange VFS performance problem

[Terry Griffin]

Hi all,

I'm having a very strange Samba VFS performance problem. Hoping
you can provide some clues.

I've implemented a custom Samba VFS module. Functionally everything
is fine and the module does what it's supposed to do.

With a Windows 2000 client the VFS module introduces an expected
throughput hit on large writes in the range of 10-20% (over Gigabit
Ethernet). But with a Linux CIFS client the throughput hit is more
like 90%!

The Linux/CIFS and W2K client throughput numbers are similar in
the case where the custom VFS module is not in use.

What about a VFS module could cause such drastically different
results between a W2K client and a Linux/CIFS client? And is there
something I can do to improve the Linux numbers? I've fiddled with
directio and CIFSMaxBufSize options on the client side with no
help. I've fiddled with all the usual tuning parameters on the Samba
side, again with no improvement.

Linux (on both the CIFS client and Samba server) is Fedora Core 2
with kernel 2.6.10. The Samba version is 3.0.10.

Thanks,
Terry