[linux-cifs-client] Slow Samba Share access to CIFS-mount - Win2k3 Share

Steven French sfrench at us.ibm.com
Wed Jul 20 16:47:13 GMT 2005






Your post did not included enough information to be conclusive about the
cause of the performance change after update of the server side to newer
Windows server version, but there are a couple things that could be done to
isolate it.   I like to use more granular performance tools (iozone e.g.,
or the connectathon "nfs" tests run in timing "-t" mode) to compare before
and after - and then compare with the network traces to see whether any
particular type of request is slower after the change.

As a long shot (in the dark) .... A new performance consideration which I
had not noticed before is TCP ack timeouts - depending on the size of the
tcp window and various issues relating to TCP's "nagle" algorithm, TCP acks
can be delayed to allow acks to be sent with subsequent requests or
responses.   This can be a disaster for performance of one process on one
client talking to one server over very high speed links since it results in
much dead time on the wire in which neither end is doing anything.
Tuning around this (e.g. changing the sizes of the request buffer via
insmod or on the server side) is a possibility and in any case is easy
enough to do that it is worth trying.   I am looking at how to disable the
nagle algorithm code on the socket on the client as well.   This may have
nothing to do with it, but I stumbled across it when I saw that a
performance improvement I had made in some cases made things an order of
magnitude slower when larger responses were sent.


Steve French
Senior Software Engineer
Linux Technology Center - IBM Austin
phone: 512-838-2294
email: sfrench at-sign us dot ibm dot com
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