linux-kernel - Re: [RFC v3 1/6] Track the active utilisation

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Date:   Tue, 8 Nov 2016 19:17:30 +0100
From:   Luca Abeni <luca.abeni@...tn.it>
To:     Juri Lelli <juri.lelli@....com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Claudio Scordino <claudio@...dence.eu.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC v3 1/6] Track the active utilisation

Hi Juri,

On Tue, 8 Nov 2016 17:56:35 +0000
Juri Lelli <juri.lelli@....com> wrote:
[...]
> > > >  static void switched_to_dl(struct rq *rq, struct task_struct
> > > > *p) {
> > > > +	add_running_bw(&p->dl, &rq->dl);
> > > >  
> > > >  	/* If p is not queued we will update its parameters at
> > > > next wakeup. */ if (!task_on_rq_queued(p))  
> > > 
> > > Don't we also need to remove bw in task_dead_dl()?
> > I think task_dead_dl() is invoked after invoking dequeue_task_dl(),
> > which takes care of this... Or am I wrong? (I think I explicitly
> > tested this, and modifications to task_dead_dl() turned out to be
> > unneeded)
> > 
> 
> Mmm. You explicitly check that TASK_ON_RQ_MIGRATING or DEQUEUE_SLEEP
> (which btw can be actually put together with an or condition), so I
> don't think that any of those turn out to be true when the task dies.
I might be very wrong here, but I think do_exit() just does something
like
	tsk->state = TASK_DEAD;
and then invokes schedule(), and __schedule() does
        if (!preempt && prev->state) {
                if (unlikely(signal_pending_state(prev->state, prev))) {
                        prev->state = TASK_RUNNING;
                } else {
                        deactivate_task(rq, prev, DEQUEUE_SLEEP);
			[...]
so dequeue_task_dl() will see DEQUEUE_SLEEP... Or am I misunderstanding
what you are saying?

> Also, AFAIU, do_exit() works on current and the TASK_DEAD case is
> handled in finish_task_switch(), so I don't think we are taking care
> of the "task is dying" condition.
Ok, so I am missing something... The state is set to TASK_DEAD, and
then schedule() is called... So, __schedule() sees the dying task as
"prev" and invokes deactivate_task() with the DEQUEUE_SLEEP flag...
After that, finish_task_switch() calls task_dead_dl(). Is this wrong?
If not, why aren't we taking care of the "task is dying" condition?


> Peter, does what I'm saying make any sense? :)
> 
> I still have to set up things here to test these patches (sorry, I was
> travelling), but could you try to create some tasks and that kill them
> from another shell to see if the accounting deviates or not? Or did
> you already do this test?
I think this is one of the tests I tried... 
I have to check if I changed this code after the test (but I do not
think I did). Anyway, tomorrow I'll write a script for automating this
test, and I'll leave it running for some hours.



				Luca