[gpfsug-discuss] iowait?

Bryan Banister bbanister at jumptrading.com
Mon Aug 29 18:56:25 BST 2016


There is the iohist data that may have what you're looking for,
-Bryan

-----Original Message-----
From: gpfsug-discuss-bounces at spectrumscale.org [mailto:gpfsug-discuss-bounces at spectrumscale.org] On Behalf Of Aaron Knister
Sent: Monday, August 29, 2016 12:54 PM
To: gpfsug-discuss at spectrumscale.org
Subject: Re: [gpfsug-discuss] iowait?

Sure, we can and we do use both iostat/sar and collectl to collect disk utilization on our nsd servers. That doesn't give us insight, though, into any individual client node of which we've got 3500. We do log mmpmon data from each node but that doesn't give us any insight into how much time is being spent waiting on I/O. Having GPFS report iowait on client nodes would give us this insight.

On 8/29/16 1:50 PM, Alex Chekholko wrote:
> 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
>>
>

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