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SubjectRe: [PATCH 0/3] pseries: Track and expose idle PURR and SPURR ticks
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Hi Kamalesh,

Kamalesh Babulal <kamalesh@linux.vnet.ibm.com> writes:
> On 12/5/19 3:54 AM, Nathan Lynch wrote:
>> "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> writes:
>>>
>>> Tools such as lparstat which are used to compute the utilization need
>>> to know [S]PURR ticks when the cpu was busy or idle. The [S]PURR
>>> counters are already exposed through sysfs. We already account for
>>> PURR ticks when we go to idle so that we can update the VPA area. This
>>> patchset extends support to account for SPURR ticks when idle, and
>>> expose both via per-cpu sysfs files.
>>
>> Does anything really want to use PURR instead of SPURR? Seems like we
>> should expose only SPURR idle values if possible.
>>
>
> lparstat is one of the consumers of PURR idle metric
> (https://groups.google.com/forum/#!topic/powerpc-utils-devel/fYRo69xO9r4).
> Agree, on the argument that system utilization metrics based on SPURR
> accounting is accurate in comparison to PURR, which isn't proportional to
> CPU frequency. PURR has been traditionally used to understand the system
> utilization, whereas SPURR is used for understanding how much capacity is
> left/exceeding in the system based on the current power saving mode.

I'll phrase my question differently: does SPURR complement or supercede
PURR? You seem to be saying they serve different purposes. If PURR is
actually useful rather then vestigial then I have no objection to
exposing idle_purr.

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