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From: Michael Ellerman <mpe@ellerman.id.au>
To: Christophe Leroy <christophe.leroy@c-s.fr>,
	Nicholas Piggin <npiggin@gmail.com>
Cc: linux-kernel@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v4 1/2] powerpc/time: Only set CONFIG_ARCH_HAS_SCALED_CPUTIME on PPC64
Date: Tue, 20 Aug 2019 22:42:39 +1000	[thread overview]
Message-ID: <87imqs57pc.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <26969bb5-c01b-0674-5773-027f1851bd44@c-s.fr>

Christophe Leroy <christophe.leroy@c-s.fr> writes:
> 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@c-s.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 ?

PURR is Power5/6/7/8/9 and PA6T (pasemi). SPURR is Power6/7/8/9.

So we could easily flip PPC64 for PPC_BOOK3S_64, which would mean 64-bit
Book3E CPUs don't get that overhead.

Beyond that is not so simple. We probably don't need that selected for
bare metal kernels (powernv). But in practice all the distros build a
multi platform kernel with powernv+pseries anyway.

We could turn it off on G5s (PPC970), by making it depend on POWERNV ||
PSERIES || PPC_PASEMI, but I'm not sure if it's worth the trouble.

cheers

      parent reply	other threads:[~2019-08-20 13:59 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-06 14:21 [PATCH v4 1/2] powerpc/time: Only set CONFIG_ARCH_HAS_SCALED_CPUTIME on PPC64 Christophe Leroy
2018-06-06 14:21 ` [PATCH v4 2/2] powerpc/time: no steal_time when CONFIG_PPC_SPLPAR is not selected Christophe Leroy
2018-06-07  1:43 ` [PATCH v4 1/2] powerpc/time: Only set CONFIG_ARCH_HAS_SCALED_CPUTIME on PPC64 Nicholas Piggin
2019-08-14  6:31   ` Christophe Leroy
2019-08-19 13:56     ` Nicholas Piggin
2019-08-20 12:42     ` Michael Ellerman [this message]

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