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Subject: Re: [RFC][PATCH 05/22] sched: SCHED_DEADLINE policy implementation
From: Peter Zijlstra <peterz@infradead.org>
To: Raistlin <raistlin@linux.it>
Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
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Date: Thu, 11 Nov 2010 15:17:03 +0100
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On Fri, 2010-10-29 at 08:30 +0200, Raistlin wrote:
> +static void update_curr_dl(struct rq *rq)
> +{
> +       struct task_struct *curr = rq->curr;
> +       struct sched_dl_entity *dl_se = &curr->dl;
> +       u64 delta_exec;
> +
> +       if (!dl_task(curr) || !on_dl_rq(dl_se))
> +               return;
> +
> +       delta_exec = rq->clock - curr->se.exec_start;
> +       if (unlikely((s64)delta_exec < 0))
> +               delta_exec = 0;
> +
> +       schedstat_set(curr->se.statistics.exec_max,
> +                     max(curr->se.statistics.exec_max, delta_exec));
> +
> +       curr->se.sum_exec_runtime += delta_exec;
> +       account_group_exec_runtime(curr, delta_exec);
> +
> +       curr->se.exec_start = rq->clock;
> +       cpuacct_charge(curr, delta_exec);
> +
> +       dl_se->runtime -= delta_exec;
> +       if (dl_runtime_exceeded(rq, dl_se)) {
> +               __dequeue_task_dl(rq, curr, 0);
> +               if (likely(start_dl_timer(dl_se)))
> +                       dl_se->dl_throttled = 1;
> +               else
> +                       enqueue_task_dl(rq, curr, ENQUEUE_REPLENISH);
> +
> +               resched_task(curr);
> +       }
> +} 

So you keep the current task in the rb-tree? If you remove the current
task from the tree you don't have to do the whole dequeue/enqueue thing.
Then again, I guess it only really matters once you push the deadline,
which shouldn't be that often.

Also, you might want to put a conditional around that resched, no point
rescheduling if you're still the leftmost task.