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

Tejun Heo
2024-06-25T23:30:08Z

Hello,

On Tue, Jun 25, 2024 at 09:49:35AM +0200, Peter Zijlstra wrote:
> > Imagine a case where a sched_ext task was running but then a RT task wakes
> > up on the CPU. We'd enter the scheduling path, RT's pick_next_task() would
> > return the new RT task to run. We now need to tell the BPF scheduler that we
> > lost the CPU to the RT task but haven't called its pick_next_task() yet.
>
> Bah, I got it backwards indeed. But in this case, don't you also need
> something in pick_task() -- the whole core scheduling thing does much
> the same.

Yes, indeed we do, but because we're dispatching from the balance path, the
cpu_acquire method is being called from there. Because who was running on
the CPU before us is less interesting, @prev is not passed into
cpu_acquire() but if that becomes necessary, it's already available there
too.

Thanks.

--
tejun