linux-kernel - Re: [PATCH 0/3] pseries: Track and expose idle PURR and SPURR ticks

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Date:   Wed, 04 Dec 2019 16:24:10 -0600
From:   Nathan Lynch <nathanl@...ux.ibm.com>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Tyrel Datwyler <tyreld@...ux.ibm.com>
Subject: Re: [PATCH 0/3] pseries: Track and expose idle PURR and SPURR ticks

"Gautham R. Shenoy" <ego@...ux.vnet.ibm.com> writes:
> From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
>
> On PSeries LPARs, the data centers planners desire a more accurate
> view of system utilization per resource such as CPU to plan the system
> capacity requirements better. Such accuracy can be obtained by reading
> PURR/SPURR registers for CPU resource utilization.
>
> 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.