From: Michael Ellerman <mpe@ellerman•id.au>
To: Balbir Singh <bsingharora@gmail•com>
Cc: linuxppc-dev@ozlabs•org, mikey@neuling•org, paulus@samba•org,
npiggin@gmail•com
Subject: Re: [PATCH] powerpc/64: Reclaim CPU_FTR_SUBCORE
Date: Tue, 30 May 2017 20:48:16 +1000 [thread overview]
Message-ID: <878tle62of.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <20170530124800.11dbc61b@firefly.ozlabs.ibm.com>
Balbir Singh <bsingharora@gmail•com> writes:
> On Mon, 29 May 2017 11:53:10 +1000
> Michael Ellerman <mpe@ellerman•id.au> wrote:
>
>> We are running low on CPU feature bits, so we only want to use them when
>> it's really necessary.
>>
>> CPU_FTR_SUBCORE is only used in one place, and only in C, so we don't
>> need it in order to make asm patching work. It can only be set on
>> "Power8" CPUs, which in practice means POWER8, POWER8E and POWER8NVL.
>> There are no plans to implement it on future CPUs, but if there ever
>> were we could retrofit it then.
>>
>> Although KVM uses subcores, it never looks at the CPU feature, it either
>> looks at the ISA level or the threads_per_subcore value.
>>
>> So drop the CPU feature and do a PVR check instead. Drop the device tree
>> "subcore" feature as we no longer support doing anything with it, and we
>> will drop it from skiboot too.
>>
>> Signed-off-by: Michael Ellerman <mpe@ellerman•id.au>
>> ---
>
> Acked-by: Balbir Singh <bsingharora@gmail•com>
>
> I looked at CPU_FTR_DBELL and its used for initialization and in
> arch_show_interrupts(), no assembly
But the other criteria is that there is a small set of CPUs where it can
be enabled, so that the PVR check is not horrible.
I don't think DBELL fits that, I see it enabled for at least Power8,
Power8E, Power9, e6500, e5500, e500mc.
cheers
next prev parent reply other threads:[~2017-05-30 10:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-29 1:53 [PATCH] powerpc/64: Reclaim CPU_FTR_SUBCORE Michael Ellerman
2017-05-30 2:48 ` Balbir Singh
2017-05-30 10:48 ` Michael Ellerman [this message]
2017-06-01 13:31 ` Michael Ellerman
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