Re: mmap() and NFS server performance

[Matthew Mitchell <matthew@geodev.com>]

Trond Myklebust wrote:
>>>>>>" " == Matthew Mitchell <matthew@geodev.com> writes:
>>>>>
> 
>      > 1) What would you like to see, tcpdump/snoop wise, to verify
>      >    this?
> 
> nfsstat on the client should normally tell you how often you are
> seeing RPC retransmits.

Ran the program again.  In 20 minutes, around 20k total client RPC 
requests, with an assortment of retrans, time, and badxid errors.  I am 
starting to believe that there is a problem using UDP, and that it alone 
might be enough to explain the slowness.   It seems to have negotiated 
an 8k transfer size.  Reasonable?

>      > 2) Could UDP service really be causing this order of magnitude
>      >    slowdown?
> 
> Certainly: retransmissions follow an *exponential* backoff rule. For
> that reason, it doesn't take a very high percentage of retransmissions
> before you see a large impact.

Seems to be borne out by the evidence.

>      > 3) Is TCP server code "ready enough" for production use?  In
>      >    our case we
>      > don't mind some occasional bugs, but it needs to be able to
>      > stay working under reasonable load for a day or so at a time
>      > for us to get anything done ("Stale NFS file handle" is a
>      > scourge...).
> 
> That is more of a question for Neil Brown, but I personally don't have
> any particularly bad experiences to report.

Any particularly *good* ones? :)  Would you recommend the 2.4.20 set, or 
some additional patches?  I will probably install the new kernel when we 
get a little downtime later this week (and then I will promptly go on 
vacation; hope it stays up! ha!).

Thanks for the suggestions and assistance.  I'll report back with TCP 
info for anyone who is interested.

-- 
Matthew Mitchell
Systems Programmer/Administrator            matthew@geodev.com
Geophysical Development Corporation         phone 713 782 1234
1 Riverway Suite 2100, Houston, TX  77056     fax 713 782 1829



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