samba - Mar 2009 - performance problem with 3.2.8: unbuffered reads for some users

Hi!

I'm experiencing strange performance problems after upgrading to samba
3.2.8 from 3.0.30.

For all users except smbadmin (who has administrative rights), read
performance is _very_ bad. Looking at the read-requests using filemon
and wireshark, I found out that for those users, every read is handled
transparently (unbuffered) over the net. (I.e. a 2 byte read-request of
the application leads to a 2 byte Read And X Request over the net.)

If the user is smbadmin, reads are block buffered. (A 2 byte
read-request of the same application as above leads to a 4096 byte Read
And X Request over the net.)

Clients are WinXP SP3.
For details, see my test below..

When are those buffering parameters negotiated? Do you have any idea why
the behavior depends on the connected user?
Any hints how I could further track down this problem?

Cheers,
--leo

The test was done using 2 byte reads on the windows box:
perl -le 'sysopen(F, "R:/firefox/LICENSE", O_RDONLY);
  do { $n= sysread(F, $buf, 2) } while ($n)'

The result can be found here:
smbadmin (buffered reads):
http://leo.kloburg.at/tmp/samba/smbadmin-tshark.txt

abergolth (unbuffered reads, same box):
http://leo.kloburg.at/tmp/samba/abergolth-tshark.txt

smb.conf
http://leo.kloburg.at/tmp/samba/smb.conf

-- 
e-mail   ::: Leo.Bergolth (at) wu-wien.ac.at
fax      ::: +43-1-31336-906050
location ::: IT-Services | Vienna University of Economics | Austria

On Wed, Mar 04, 2009 at 01:56:26PM +0100, Alexander 'Leo' Bergolth
wrote:
> I'm experiencing strange performance problems after upgrading to samba
> 3.2.8 from 3.0.30.
> 
> For all users except smbadmin (who has administrative rights), read
> performance is _very_ bad. Looking at the read-requests using filemon
> and wireshark, I found out that for those users, every read is handled
> transparently (unbuffered) over the net. (I.e. a 2 byte read-request of
> the application leads to a 2 byte Read And X Request over the net.)
> 
> If the user is smbadmin, reads are block buffered. (A 2 byte
> read-request of the same application as above leads to a 4096 byte Read
> And X Request over the net.)
> 
> Clients are WinXP SP3.
> For details, see my test below..
Unfortunately, the log files do not show enough information
about what is happening. Simple tshark output is not
sufficient, see
http://wiki.samba.org/index.php/Capture_Packets for more
information on creating useful sniffs.
> When are those buffering parameters negotiated? Do you have any idea why
> the behavior depends on the connected user?
If it really depends on the connected user, then we need a
debug level 10 log of smbd doing it. I would however suspect
that this depends on the fact if a file is shared between
two users or two applications on the same client box or not.
If this is the case, then it is intended behaviour, because
the clients lost their oplocks. You might need to
restructure your application to not do 2 byte read requests.

Volker
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