Re: [PATCH v4 3/5] sched/fair: Switch to task based throttle model

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Sep 05, 2025 at 07:37:19PM +0800, Aaron Lu wrote:
> Hi Peter,
> 
> On Thu, Sep 04, 2025 at 03:04:07PM +0800, Aaron Lu wrote:
> > On Thu, Sep 04, 2025 at 11:14:31AM +0530, K Prateek Nayak wrote:
> > > On 9/4/2025 1:57 AM, Peter Zijlstra wrote:
> > > > So this is mostly tasks leaving/joining the class/cgroup. And its
> > > > purpose seems to be to remove/add the blocked load component.
> > > > 
> > > > Previously throttle/unthrottle would {de,en}queue the whole subtree from
> > > > PELT, see how {en,de}queue would also stop at throttle.
> > > > 
> > > > But now none of that is done; PELT is fully managed by the tasks
> > > > {de,en}queueing.
> > > > 
> > > > So I'm thinking that when a task joins fair (deboost from RT or
> > > > whatever), we add the blocking load and fully propagate it. If the task
> > > > is subject to throttling, that will then happen 'naturally' and it will
> > > > dequeue itself again.
> > > 
> > > That seems like the correct thing to do yes. Those throttled_cfs_rq()
> > > checks in propagate_entity_cfs_rq() can be removed then.
> > >
> > 
> > Not sure if I understand correctly, I've come to the below code
> > according to your discussion:
> >
> 
> Does the below diff look sane to you? If so, shall I send a separate
> patch on top or fold it in patch3 and send an updated patch3?

Yeah, I suppose that works. Please send a follow up patch. It would also
be good to have a comment that explains why we need that list_add_leaf
thing. I think I see, but I'm sure I'll have forgotten all next time I
see this code.