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Date:   Wed, 05 Feb 2020 13:37:45 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [PATCH 2/3] powerpc/sysfs: Show idle_purr and idle_spurr for
 every CPU
To:     Christophe Leroy <christophe.leroy@c-s.fr>,
        "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>,
        Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nathan Lynch <nathanl@linux.ibm.com>,
        Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
        Tyrel Datwyler <tyreld@linux.ibm.com>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
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Christophe Leroy wrote:
> 
> 
> Le 27/11/2019 à 13:01, Gautham R. Shenoy a écrit :
>> From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
>> 
>> On Pseries LPARs, to calculate utilization, we need to know the
>> [S]PURR ticks when the CPUs were busy or idle.
>> 
>> The total PURR and SPURR ticks are already exposed via the per-cpu
>> sysfs files /sys/devices/system/cpu/cpuX/purr and
>> /sys/devices/system/cpu/cpuX/spurr.
>> 
>> This patch adds support for exposing the idle PURR and SPURR ticks via
>> /sys/devices/system/cpu/cpuX/idle_purr and
>> /sys/devices/system/cpu/cpuX/idle_spurr.
> 
> Might be a candid question, but I see in arch/powerpc/kernel/time.c that 
> PURR/SPURR are already taken into account by the kernel to calculate 
> utilisation when CONFIG_VIRT_CPU_ACCOUNTING_NATIVE is selected.
> 
> As far as I understand, you are wanting to expose this to userland to 
> redo the calculation there. What is wrong with the values reported by 
> the kernel ?

As you point out, it is only done with 
CONFIG_VIRT_CPU_ACCOUNTING_NATIVE, but isn't available with NO_HZ_FULL, 
which happens to be the distro default nowadays.

- Naveen