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Subjectbdflush/rpciod high CPU utilization, profile does not make sense

Hello list,

NFS server (dual opteron, HW RAID, SCA disk enclosure) on
NFS client (dual PIII) on

Both on switched gigabit ethernet - I use NFSv3 over UDP (tried TCP but
this makes no difference).

Problem; during simple tests such as a 'cp largefile0 largefile1' on the
client (under the mountpoint from the NFS server), the client becomes
extremely laggy, NFS writes are slow, and I see very high CPU
utilization by bdflush and rpciod.

For example, writing a single 8G file with dd will give me about
20MB/sec (I get 60+ MB/sec locally on the server), and the client rarely
drops below 40% system CPU utilization.

I tried profiling the client (booting with profile=2), but the profile
traces do not make sense; a profile from a single write test where the
client did not at any time drop below 30% system time (and frequently
were at 40-50%) gives me something like:

raven:~# less profile3 | sort -nr | head
257922 total 2.6394
254739 default_idle 5789.5227
960 smp_call_function 4.0000
888 __might_sleep 5.6923
569 finish_task_switch 4.7417
176 kmap_atomic 1.7600
113 __wake_up 1.8833
74 kmap 1.5417
64 kunmap_atomic 5.3333

The difference between default_idle and total is 1.2% - but I never saw
system CPU utilization under 30%...

Besides, there's basically nothing in the profile that rhymes with
rpciod or bdflush (the two high-hitters on top during the test).

What do I do?

Performance sucks and the profiles do not make sense...

Any suggestions would be greatly appreciated,

Thank you!


/ jakob

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