On 19/08/25 12:34, Gabriele Monaco wrote:

On Tue, 2025-08-19 at 12:12 +0200, Peter Zijlstra wrote:

quoted

On Tue, Aug 19, 2025 at 11:56:57AM +0200, Juri Lelli wrote:

quoted

Hi!

On 14/08/25 17:08, Gabriele Monaco wrote:

...

quoted

quoted

quoted

@@ -1482,6 +1486,7 @@ static void update_curr_dl_se(struct rq

*rq, struct sched_dl_entity *dl_se, s64
 
 throttle:
 	if (dl_runtime_exceeded(dl_se) || dl_se->dl_yielded) {
+		trace_sched_dl_throttle_tp(dl_se);
 		dl_se->dl_throttled = 1;

I believe we also need to trace the dl_check_constrained_dl()
throttle, please take a look.

Probably yes, strangely I couldn't see failures without it, but it may
be down to my test setup. I'm going to have a look.

Not sure if you tested with constrained (deadline != period) tasks.

quoted

quoted

Also - we discussed this point a little already offline - but I
still wonder if we have to do anything special for dl-server defer.
Those entities are started as throttled until 0-lag, so maybe we
should still trace them explicitly as so?

The naming might need a bit of a consistency check here, but for the
monitor, the server is running, armed or preempted. Before the 0-lag,
it will never be running, so it will stay as armed (fair tasks running)
or preempted (rt tasks running).

armed and preempted have the _throttled version just to indicate an
explicit throttle event occurred.

We might want to start it in the armed_throttled if we are really
guaranteed not to see a throttle event, but I think that would
complicate the model considerably.

We could instead validate the 0-lag concept in a separate, server-
specific model.

Does this initial model feel particularly wrong for the server case?

No it doesn't atm. :-) Thanks for the additional information.

quoted

quoted

In addition, since it's related, maybe we should do something about
sched_switch event, that is currently not aware of deadlines,
runtimes, etc.

I'm not sure I follow you here, what relation with switch and
runtime/deadline should we enforce?

We don't really force the switch to occur timely after throttling, is
that what you mean?
Or a switch must occur again timely after replenishing?

Hummm, yeah I was wondering if we need something along these lines, but
we can also maybe leave it for the future.

quoted

As per the whole _tp() thing, you can attach to the actual
sched_switch tracepoint with a module and read whatever you want.

Yeah I believe Juri referred to model constraints on the already
existing events rather than new tracepoints here.

Separately from this series, maybe we should put such a module/bpf thing
somewhere shared, so it's easier to use it when needed.