2.4 vs. 2.6 nfs client performance

[Jason Holmes <jholmes@psu.edu>]

Hi,

I'm running some NFS performance tests to determine the best way to go
to configure a few fileservers for some linux clusters I run.  Right now
I'm getting together a suite of test programs representative of the
typical applications we see run on our clusters (scientific applications
such as Ansys or Abaqus, custom MPI code, etc.) for use as a benchmark
suite that I can disperse across 16 machines or so to create a decent
load on the fileservers.  I've just got started with a program called
Gaussian03 (molecular modelling code that does a lot of I/O) and I'm
already seeing some odd performance differences between the 2.4.22
client and the 2.6.0-test9-mm1 client (both against a 2.6.0-test9-mm2
server):

async mounts
------------
2.4.22:           110.87user 43.69system 4:04.58elapsed 63%CPU
2.6.0-test9-mm1:  111.88user 315.57system 9:51.87elapsed 72%CPU

sync mounts
-----------
2.4.22:           109.99user 45.49system 32:04.44elapsed 8%CPU
2.6.0-test9-mm1:  112.33user 197.76system 1:08:13elapsed 7%CPU

Note that the 1:08:13 in the sync 2.6.0-test9-mm1 is 1 *hour*, 8
minutes, not 1 *minute*.  In both cases the 2.6 client came in at about
twice the time.  A local run not using NFS finishes in 2:13.49.

The nfsstats output for two async runs looks like:

-- 2.4.22 --
Client nfs v3:
null       getattr    setattr    lookup     access     readlink
0       0% 880     0% 0       0% 160     0% 4745    0% 0       0%
read       write      create     mkdir      symlink    mknod
780     0% 178588 32% 24      0% 0       0% 0       0% 0       0%
remove     rmdir      rename     link       readdir    readdirplus
24      0% 0       0% 0       0% 0       0% 18      0% 0       0%
fsstat     fsinfo     pathconf   commit
3       0% 3       0% 0       0% 369185 66%

Client rpc stats:
calls      retrans    authrefrsh
554410     2099       0


-- 2.6.0-test9-mm1 --

Client nfs v3:
null       getattr    setattr    lookup     access     readlink
0       0% 740     0% 0       0% 126     0% 249     0% 0       0%
read       write      create     mkdir      symlink    mknod
855     0% 178574 14% 24      0% 0       0% 0       0% 0       0%
remove     rmdir      rename     link       readdir    readdirplus
24      0% 0       0% 0       0% 0       0% 18      0% 0       0%
fsstat     fsinfo     pathconf   commit
0       0% 3       0% 0       0% 1023777 85%

Client rpc stats:
calls      retrans    authrefrsh
1204390    5          0

The 2.6 client has over twice the number of RPC calls and almost 3 times
the number of commits whereas the 2.4 client has alot more accesses. 
Mounts were done with rsize=32768,wsize=32768.  The NFS filesystem is
ext3.  The two machines are connected via gigabit ethernet and the
traffic between them never goes above 20-30 MB/s.

Can someone clue me in as to why this may be happening and if it's a
"bug" or not?

Thanks,

--
Jason Holmes


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