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

[Christoph Lameter (Ampere)]

On Tue, 4 Aug 2026, David Hildenbrand (Arm) wrote:

> > rather hacky restart logic. It relies on a long preemable and postscript
> > to each per cpu operations.

> 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.

The comparison here is a single instruction on one side and abnd the per
cpu operation prefixed with a preeamble and another instruction / set of
instructions on the other side.

Even if its only one before and one after then we are still looking at 3
instructions instead of one. This is a frequently used operation in the
VM.

You need data to show that one instruction  is faster than 3???

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

Well there is interest by the S390 folks to move to what we proposed from
what I can tell.


> 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.

You cannot accept that one instruction is faster than the same
instruction prefixed with another and something else at its tail?