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SubjectSlow NFS reading with multiple clients

Hello,

I am resending that post since it has had no echo and seemed to hide some
problem.

I have installed the RH 6.0 on a Linux NFS server and updated the kernel
to 2.2.7-ac1.

I am testing NFS with iozone.

The NFS server is doing rather well with one client (6,8Mo/s with a
2.2.{6,7}-ac1 Linux client, 7,3 Mo/s with a FreeBSD client for writing,
4,5 Mo/s during reading for Linux, 4,8 Mo/s for FreeBSD).

Unfortunately, when I run two clients at the same time, reading
performance drops drastically : 700 Ko/s each. During rereading,
the load of the server climbs between 4 and 5. With 1 client, the
load during reading ist around 0,20.

When I run two iozones locally on the server, I get 3,5 Mo/s on each
iozone (ie, the global rate is around 7 Mo/s, which is consistent).

So, to summary :

1) 1 NFS client : ~ 7 Mo/s writing, 5 Mo/s reading
2) 2 NFS clients: ~ 7 Mo/s writing, 1,5 Mo/s reading (cumulated : BAD)

3) 1 local client : ~ 9 Mo/s writing, 7 Mo/s reading
4) 2 local clients : ~ 9 Mo/s writing, 7 Mo/s reading. (cumulated : OK)

Where can the problem (1,5 Mo/s) be ?

I tried with 2.2.6-ac1 on the server, without any change.

No process seems to eat that much CPU :

> 7:32pm up 18 min, 1 user, load average: 6.95, 3.91, 2.09
> 47 processes: 44 sleeping, 3 running, 0 zombie, 0 stopped
> CPU states: 0.1% user, 1.7% system, 0.0% nice, 98.0% idle
> Mem: 63392K av, 61900K used, 1492K free, 2536K shrd, 1320K buff
> Swap: 120480K av, 4372K used, 116108K free 56472K cached
>
> PID USER PRI NI SIZE RSS SHARE STAT LIB %CPU %MEM TIME COMMAND
> 485 root 2 0 0 0 0 DW 0 0.3 0.0 0:10 nfsd
> 486 root 1 0 0 0 0 DW 0 0.3 0.0 0:09 nfsd
> 973 danis 2 0 488 448 336 R 0 0.3 0.7 0:04 top
> 483 root 1 0 0 0 0 DW 0 0.1 0.0 0:10 nfsd
> 484 root 1 0 0 0 0 DW 0 0.1 0.0 0:10 nfsd
> 487 root 2 0 0 0 0 DW 0 0.1 0.0 0:10 nfsd
> 488 root 1 0 0 0 0 DW 0 0.1 0.0 0:09 nfsd
...

A +,
--
Thierry Danis

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