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 for <linuxppc-dev@lists.ozlabs.org> from <aneesh.kumar@linux.vnet.ibm.com>;
 Tue, 27 Feb 2018 04:00:20 -0000
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: Nicholas Piggin <nicholas.piggin@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>, paulus@samba.org,
 mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH V2] powerpc: Don't do runtime futex_cmpxchg test
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 <CANashXPc952+httE=Vhx=wGrkN3Ycva7j+a+WE6jXQaw38p=YQ@mail.gmail.com>
Date: Tue, 27 Feb 2018 09:30:15 +0530
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Nicholas Piggin <nicholas.piggin@gmail.com> writes:

> On 27 Feb. 2018 00:34, "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> wrote:
>
> futex_detect_cmpxchg() does a cmpxchg_futex_value_locked on a NULL user
> addr to
> runtime detect whether architecture implements atomic cmpxchg for futex.
> POWER
> do implement the feature and hence we can enable the config instead of
> depending
> on runtime detection.
>
> We could possible enable this on everything. For now limitted to book3s_64
>
>
> I think everything implements it? Might as well do it all at once.
>
> I wouldn't mind putting in an explicit null dereference test if we take
> this out.

If the config is not selected we do that with futex_detect_cmpxchg()
right? Or are you suggesting something else?

>
> Thanks,
> Nick
>
>
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> ---
>  arch/powerpc/platforms/Kconfig.cputype | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/powerpc/platforms/Kconfig.cputype
> b/arch/powerpc/platforms/Kconfig.cputype
> index a429d859f15d..31bc2bd5dfd1 100644
> --- a/arch/powerpc/platforms/Kconfig.cputype
> +++ b/arch/powerpc/platforms/Kconfig.cputype
> @@ -75,6 +75,7 @@ config PPC_BOOK3S_64
>         select ARCH_SUPPORTS_NUMA_BALANCING
>         select IRQ_WORK
>         select HAVE_KERNEL_XZ
> +       select HAVE_FUTEX_CMPXCHG if FUTEX
>
>  config PPC_BOOK3E_64
>         bool "Embedded processors"
> --
> 2.14.3