Re: [PATCH 0/7] CPU controller - V1

Srivatsa Vaddagiri
2006-08-21T16:46:39Z

On Mon, Aug 21, 2006 at 05:10:41PM +0000, Mike Galbraith wrote:
> I must be missing something. If current and awakening tasks have
> separate runqueues, task_rq(awakening)->curr != current. We won't look
> at current->prio, so won't resched(current).

Ok ..we have two types of runqueues here:

1. struct task_grp_rq
per-task-group-per-cpu runqueue, which holds ready-to-run tasks
belonging to the group in active and expired arrays.

2. struct rq
per-cpu runqueue, which holds ready-to-run task-groups in active and
expired arrays. This structure also holds some members like
curr, nr_running etc which more or less have the same significance as
the current runqueue members.

task_rq(tsk) still extracts "struct rq", while
task_grp(tsk)->rq[task_cpu(tsk)] extracts "struct task_grp_rq".

Hence task_rq(awakening)->curr == current, which should be sufficient to
resched(current), although I think there is a bug in current code
(irrespective of these patches):

try_to_wake_up() :

...

if (!sync || cpu != this_cpu) {
if (TASK_PREEMPTS_CURR(p, rq))
resched_task(rq->curr);
}
success = 1;

...

TASK_PREEMPTS_CURR() is examined and resched_task() is called only if
(cpu != this_cpu). What about the case (cpu == this_cpu) - who will
call resched_task() on current? I had expected the back-end of interrupt
handling to do that, but didnt find any code to do so.

--
Regards,
vatsa