Messages in this thread |  | | Date | Fri, 06 Dec 2019 14:44:06 +0530 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH 0/3] pseries: Track and expose idle PURR and SPURR ticks |
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Naveen N. Rao wrote: > 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.
Re-reading this today morning, I realize that this isn't entirely accurate. SPURR alone is sufficient to understand core resource utilization.
Kamalesh is using PURR to display non-normalized utilization values (under 'actual' column), as reported by lparstat on AIX. I am not entirely sure if it is ok to derive these based on the SPURR busy/idle ratio.
- Naveen
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