From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
To: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
Nathan Lynch <nathanl@linux.ibm.com>
Cc: Tyrel Datwyler <tyreld@linux.ibm.com>,
"Gautham R. Shenoy" <ego@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org,
Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 0/3] pseries: Track and expose idle PURR and SPURR ticks
Date: Fri, 06 Dec 2019 14:44:06 +0530 [thread overview]
Message-ID: <1575623305.dgcux6u43j.naveen@linux.ibm.com> (raw)
In-Reply-To: <1575566328.nhfi897fmd.naveen@linux.ibm.com>
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
next prev parent reply other threads:[~2019-12-06 9:16 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-27 12:01 [PATCH 0/3] pseries: Track and expose idle PURR and SPURR ticks Gautham R. Shenoy
2019-11-27 12:01 ` [PATCH 1/3] powerpc/pseries: Account for SPURR ticks on idle CPUs Gautham R. Shenoy
2019-12-03 13:39 ` Kamalesh Babulal
2019-12-04 22:24 ` Nathan Lynch
2020-02-03 4:45 ` Gautham R Shenoy
2019-11-27 12:01 ` [PATCH 2/3] powerpc/sysfs: Show idle_purr and idle_spurr for every CPU Gautham R. Shenoy
2019-12-03 13:37 ` Kamalesh Babulal
2019-12-04 12:37 ` Gautham R Shenoy
2019-12-03 21:02 ` kbuild test robot
2019-12-04 22:24 ` Nathan Lynch
2020-02-03 4:47 ` Gautham R Shenoy
2019-12-05 16:53 ` Naveen N. Rao
2020-02-03 4:50 ` Gautham R Shenoy
2020-02-04 7:52 ` Naveen N. Rao
2020-02-05 4:19 ` Gautham R Shenoy
2020-02-05 6:58 ` Naveen N. Rao
2020-02-05 7:08 ` Christophe Leroy
2020-02-05 8:07 ` Naveen N. Rao
2019-11-27 12:01 ` [PATCH 3/3] Documentation: Document sysfs interfaces purr, spurr, idle_purr, idle_spurr Gautham R. Shenoy
2019-12-04 22:25 ` Nathan Lynch
2019-12-04 22:24 ` [PATCH 0/3] pseries: Track and expose idle PURR and SPURR ticks Nathan Lynch
2019-12-05 15:03 ` Kamalesh Babulal
2019-12-05 16:16 ` Nathan Lynch
2019-12-05 17:25 ` Naveen N. Rao
2019-12-06 9:14 ` Naveen N. Rao [this message]
2020-02-04 9:12 ` Kamalesh Babulal
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