Re: [PATCH sched_ext/for-6.11] sched, sched_ext: Replace scx_next_task_picked() with sched_class->switch_class()

Tejun Heo
2024-06-21T19:46:58Z

Hello,

On Thu, Jun 20, 2024 at 03:42:48PM -0700, Linus Torvalds wrote:
...
> Btw, indirect calls are now expensive enough that when you have only a
> handful of choices, instead of a variable
>
> class->some_callback(some_arguments);
>
> you might literally be better off with a macro that does
>
> #define call_sched_fn(class, name, arg...) switch (class) { \
> case &fair_name_class: fair_name_class.name(arg); break; \
> ... unroll them all here..
>
> which then just generates a (very small) tree of if-statements.
>
> Again, this is entirely too ugly to do unless people *really* care.
> But for situations where you have a small handful of cases known at
> compile-time, it's not out of the question, and it probably does
> generate better code.

I'll update the patch description to point to the previous message just in
case and apply it to sched_ext/for-6.11.

Thanks.

--
tejun