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

From: Srivatsa Vaddagiri
Date: Mon Aug 21 2006 - 12:44:29 EST

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) {
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.

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