Re: [PATCH] xen/livepatch: Make check_for_livepatch_work() faster in the common case

[Ross Lagerwall <ross.lagerwall@xxxxxxxxx>]

On Fri, Dec 22, 2023 at 10:01 PM Andrew Cooper
<andrew.cooper3@xxxxxxxxxx> wrote:
>
> When livepatching is enabled, this function is used all the time.  Really do
> check the fastpath first, and annotate it likely() as this is the right answer
> 100% of the time (to many significant figures).
>
> This cuts out 3 pointer dereferences in the "nothing to do path", and it seems
> the optimiser has an easier time too.  Bloat-o-meter reports:
>
>   add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-57 (-57)
>   Function                                     old     new   delta
>   check_for_livepatch_work.cold               1201    1183     -18
>   check_for_livepatch_work                    1021     982     -39
>
> which isn't too shabby for no logical change.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>