linux-kernel - Re: [PATCH v4 1/2] powerpc/time: Only set CONFIG_ARCH_HAS_SCALED

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Date:   Mon, 19 Aug 2019 23:56:43 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Segher Boessenkool <segher@...nel.crashing.org>
Subject: Re: [PATCH v4 1/2] powerpc/time: Only set
 CONFIG_ARCH_HAS_SCALED_CPUTIME on PPC64

Christophe Leroy's on August 14, 2019 4:31 pm:
> Hi Nick,
> 
> 
> Le 07/06/2018 à 03:43, Nicholas Piggin a écrit :
>> On Wed,  6 Jun 2018 14:21:08 +0000 (UTC)
>> Christophe Leroy <christophe.leroy@....fr> wrote:
>> 
>>> scaled cputime is only meaningfull when the processor has
>>> SPURR and/or PURR, which means only on PPC64.
>>>
> 
> [...]
> 
>> 
>> I wonder if we could make this depend on PPC_PSERIES or even
>> PPC_SPLPAR as well? (That would be for a later patch)
> 
> Can we go further on this ?
> 
> Do we know exactly which configuration support scaled cputime, in 
> extenso have SPRN_SPURR and/or SPRN_PURR ?
> 
> Ref https://github.com/linuxppc/issues/issues/171

Unfortunately I don't know enough about the timing stuff and who
uses it. SPURR is available on all configurations (guest, bare metal),
so it could account scaled time there too. I guess better just leave
it for now.

Thanks,
Nick