[Samba] performance regression between 30.14a and 3.0.20

[Jeremy Allison]

On Wed, Apr 26, 2006 at 01:20:23PM -0400, Greg Dickie wrote:
> OK all my gobbledy-gook stats aside..... sorry for being incoherent.
> 
> Stracing reveals that files after 3.0.20b are opened with O_SYNC. Could 
> that be the source of the problems? I'll try and find that and test it 
> when I get home but the question is is it necessary?

Greg - I LOVE YOU :-). That's almost certainly the problem.
Back in the Win9x protocols days (the openX style of calls)
we had the problem that Windows clients were setting the 
"sync this data" flag for almost every open - completely
unneccessary. For 3.0.20x we changed to the NTcreateX
style of open, and mapped the create option FILE_WRITE_THROUGH
to the O_SYNC. I bet the Windows redirector in W2K, XP and W2K3
is just as dim, and is adding that on almost every open (I'm
on a plane right now so can't get to my vmware sessions
easily to check).

We have an option "strict sync" which if unset allows us
to ignore these calls - I've just added it into the ntcreate
open path so we don't set O_SYNC unless "strict sync" is
set.

Please check out SAMBA_3_0 and test - this will be in the
next 3.0.23 pre-release.

Jeremy.