[Lustre-discuss] copy_user_generic_c ?

[Kalpak Shah]

On Tue, 2008-07-08 at 09:46 -0400, Roger Spellman wrote:
> > Yes, by all means it shouldn't need a copy on the OST - that is what
> > RDMA is for.  
> 
> Agreed!
> 
> > You definitely are not running Samba exports on the OST
> > node?  
> 
> Certainly not.
> 
> I can't imagine what else would be doing this on an OST.
> 
> > Your oprofile output should be able to show the callchain for the
> > busiest callpaths.  Alternately, if this is active 25% of the time it
> > may be enough to do "echo p > /proc/sysrq-trigger" 16 times and see
> > what the resulting stacks are.  In theory 4 of them should have
> > copy_{to,from}_user() at the top of the stack.
> 
> Andreas, why would 4 threads have copy_(to,from)_user at the top of the
> stack?  Are certain threads supposed to be doing that on an OST?

Since the CPU on the OST is active 25% of the time, triggering a stack
trace 16 times, should give us the stack trace for the
copy_{to,from}_user() functions around 4 times.

I don't think copy_{to,from}_user() is expected to be called on the OST
with that frequency(if any) so having the stack trace will help us
determine from where it is being called.

Thanks,
Kalpak

> 
> Thanks,
> 
> Roger
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