On Mon, Dec 12, 2022 at 12:28:29PM +0100, Peter Zijlstra wrote: > On Tue, Nov 29, 2022 at 10:22:48PM -1000, Tejun Heo wrote: > > When a task switches to a new sched_class, the prev and new classes are > > notified through ->switched_from() and ->switched_to(), respectively, after > > the switching is done. However, a new sched_class needs to prepare the task > > state before it is enqueued on the new class for the first time. > > How and why isn't sched_fork() sufficient? sched_ext has callbacks which allow the BPF scheduler to keep track of relevant task states (like priority and cpumask). Those callbacks aren't called while a task isn't on sched_ext. When a task comes back to SCX, we wanna tell the BPF scheduler the up-to-date state before the task gets enqueued, so the need for a hook which is called before the switching is committed. Thanks. -- tejun
