Re: [RFC v2 PATCH 0/16] Optimize this_cpu_*() ops for non-x86 (ARM64 for this series)

[David Hildenbrand (Arm)]

On 8/4/26 18:19, Christoph Lameter (Ampere) wrote:
> On Tue, 4 Aug 2026, Lorenzo Stoakes (ARM) wrote:
> 
>> Since this work seems to be very much arm64-focused, perhaps it's therefore
>> worth looking at an alterative solution that's specific to the arch, like the
>> one suggested by Mark ([1])?
>>
>> [0]:https://lore.kernel.org/all/CAHk-=wire3dzhHx=KiL_f5Rj0=1u9ustsa33QoR-F9-v-NU9Ng@xxxxxxxxxxxxxx/
>> [1]:https://lore.kernel.org/linux-arm-kernel/al_DpFJFcmVhxpvW@J2N7QTR9R3/
> 
> Mark's solution does replace the preempt_enable/disable sections with a
> rather hacky restart logic. It relies on a long preemable and postscript
> to each per cpu operations.

Okay, so 3 simple instructions of preemable is "long preemable"? In which universe?

But I am sure you did you homework and have data to back up your claims. Please
share that data, because I am very curious.

> 
>  It does not remove the code entirely like the proposed patchset here and
> cannot produce the same compact code as x86.

Mark's solution is the obvious improvement to the problem, doing it just like
s390 already does.

If the proposed solution has a significant benefit over Mark's solution it could
be discussed as a next step; and it must be backed with sufficient data to
warrant all this complexity here.

-- 
Cheers,

David