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

Peter Zijlstra
2024-06-24T09:04:49Z

On Fri, Jun 21, 2024 at 09:46:56AM -1000, Tejun Heo wrote:
> 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.

Can you please back merge and keep it a sane series? I'm going to have
to review it (even though I still very strongly disagree with the whole
thing) and there really is nothing worse than a series that introduces
things only to remove/change them again later.