Re: [PATCH v3 08/11] slub: Replace cmpxchg_double()

Arnd Bergmann
2023-05-25T10:52:44Z

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