[gpfsug-discuss] iowait?

[Aaron Knister]

Hi Everyone,

Would it be easy to have GPFS report iowait values in linux? This would 
be a huge help for us in determining whether a node's low utilization is 
due to some issue with the code running on it or if it's blocked on I/O, 
especially in a historical context.

I naively tried on a test system changing schedule() in 
cxiWaitEventWait() on line ~2832 in gpl-linux/cxiSystem.c to this:

again:
   /* call the scheduler */
   if ( waitFlags & INTERRUPTIBLE )
     schedule();
   else
     io_schedule();

Seems to actually do what I'm after but generally bad things happen when 
I start pretending I'm a kernel developer.

Any thoughts? If I open an RFE would this be something that's relatively 
easy to implement (not asking for a commitment *to* implement it, just 
that I'm not asking for something seemingly simple that's actually 
fairly hard to implement)?

-Aaron

-- 
Aaron Knister
NASA Center for Climate Simulation (Code 606.2)
Goddard Space Flight Center
(301) 286-2776