From: Andrew Ryan <andrewr@nam-shub.com>
Subject: 3 bugs with UDP mounts
Date: Sun, 21 Apr 2002 12:06:53 -0700
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Running performance tests on NFS this past week, I've uncovered 3 apparent 
bugs. The first bug is pretty unpleasant, but the second two are fairly minor.

kernel: 2.4.17+NFS-ALL-2002-Jan-17, 2.4.19pre7+NFS-ALL. Both SMP on a 2-CPU 
system.
nfs-utils-0.3.1-13.7.2.1, mount-2.11g-5
server: NetApp
network: 100baseTx-FD on client, gigE-FD on server

1. UDP read performance (v2 and v3) on large files is really poor. I first 
noticed this problem when trying to get bonnie++ and tiobench results and 
seeing runs which should take about 20 minutes take 24+ hours. To duplicate 
this, I created a 1600MB file filled with zeros, and this went quickly. 
While writing the file, on the server I saw ~500 NFS ops/sec, and about 
4400 kB/s in on the network interface. When I tried reading the file back, 
with 'cat /path/to/file > /dev/null' I saw initially fast reads; 7900kB/s 
for a few seconds, then slowing down to 100kB/s and ~100 NFSops/sec after a 
few seconds.

I can get excellent read performance, as long as the files are relatively 
small. With a Solaris client, mounting the same server UDP (and also 
100baseTx-FD), reading the same file is done at a consistently high speed, 
so it definitely seems to be a linux-specific problem.


2. I accidentally mounted an NFS filesystem 
"udp,nfsvers=3,rsize=32768,wsize=32768". For one, I don't exactly 
understand why this was allowed, since it doesn't seem like I should be 
allowed to mount NFS/UDP with these options. Also, this creates a 
disagreement between what is returned by the 'mount' command and 'cat 
/proc/mounts'.

The relevant line from the 'mount' command shows this:
fileserver:/vol/stage/data on /shared/data type nfs 
(rw,udp,nfsvers=3,rsize=32768,wsize=32768,intr,hard,addr=192.168.100.240)

while the relevant line from /proc/mounts shows this:
fileserver:/vol/stage/data /shared/data nfs 
rw,v3,rsize=8192,wsize=8192,hard,intr,udp,lock,addr=fileserver 0 0
This may be a problem with my version of mount or nfs-utils, anyone seen 
this before?


3. Running the cthon02 tests with UDP/v3 I get one failure. This looks like 
a trivial problem to fix, if in fact it is a problem and not just a 
disagreement about how the spec is interpreted.
Test #6 - Try to lock the MAXEOF byte.
         Parent: 6.0  - F_TLOCK [7fffffff,       1] PASSED.
         Child:  6.1  - F_TEST  [7ffffffe,       1] PASSED.
         Child:  6.2  - F_TEST  [7ffffffe,       2] FAILED!
         Child:  **** Expected EACCES, returned EOVERFLOW...
         Child:  **** Probably implementation error.


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