Messages in this thread |  | | Date | Thu, 05 Dec 2019 22:55:05 +0530 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH 0/3] pseries: Track and expose idle PURR and SPURR ticks |
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Hi Nathan,
Nathan Lynch wrote: > 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.
SPURR complements PURR, so we need both. SPURR/PURR ratio helps provide an indication of the available headroom in terms of core resources, at maximum frequency.
- Naveen
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