Re: [RFC PATCH 00/18] mm: arm64: Add kernel replication feature

[David Hildenbrand (Arm)]

[...]

About to go on PTO, some random points :)

> 
>> [12] - Optimize this_cpu_*() ops for non-x86 (ARM64 for this series)
>>
>> As of today, none of it was merged into mainline.
> 
> I mean :) maybe take that as a hint? If a number of series trying to do X get
> rejected by upstream, that is maybe suggestive of barking up the wrong tree?

I'd have expected an explanation at that point why previous approaches were not
merged and how this patch set is sufficiently different that it is worth
maintainer's time.

> 
>> However, after thorough re-evaluation, we were not able to observe
>> performance improvement for the x86 platform, so we have decided to stop this
>> direction and switch on arm64.
> 
> I mean, why? You should provide details here, this is quite hand-wavey. You are
> also proposing core mm changes for something that seems specific to unique
> hardware as far as I can tell, which is a big ask.

What I consider interesting is "after thorough re-evaluation, we were not able
to observe performance improvement for the x86 platform".

How confident are we that a thorough re-evaluation on arm64 will not similarly
have the same outcome? IOW, what was the problematic part when doing the x86
evaluation, and how was that avoided when evaluating the arm64 implementation?

-- 
Cheers,

David