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Date:   Thu, 25 May 2023 12:52:06 +0200
From:   "Arnd Bergmann" <arnd@arndb.de>
To:     "Peter Zijlstra" <peterz@infradead.org>,
        "Linus Torvalds" <torvalds@linux-foundation.org>
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Subject: Re: [PATCH v3 08/11] slub: Replace cmpxchg_double()
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On Thu, May 25, 2023, at 12:29, Peter Zijlstra wrote:
> On Wed, May 24, 2023 at 11:32:47AM +0200, Peter Zijlstra wrote:
>> On Mon, May 15, 2023 at 09:57:07AM +0200, Peter Zijlstra wrote:
>
> This then also means I need to look at this_cpu_cmpxchg128 and
> this_cpu_cmoxchg64 behaviour when we dont have the CPUID feature.
>
> Because current verions seem to assume the instruction is present.

As far as I could tell when reviewing your series, this_cpu_cmpxchg64()
is always available on all architectures. Depending on compile-time
feature detection this would be either a native instruction that
is guaranteed to work, or the irq-disabled version. On x86, this
is handled at runtime with alternative_io().

this_cpu_cmpxchg128() clearly needed the system_has_cmpxchg128()
check, same as system_has_cmpxchg_double() today.

     Arnd