[gpfsug-discuss] iowait?

Alex Chekholko chekh at stanford.edu
Mon Aug 29 18:50:23 BST 2016


Any reason you can't just use iostat or collectl or any of a number of 
other standards tools to look at disk utilization?

On 08/29/2016 10:33 AM, Aaron Knister wrote:
> 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
>

-- 
Alex Chekholko chekh at stanford.edu




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