* Kirill Tkhai <[email protected]> wrote:
> v5: New names: TASK_ON_RQ_QUEUED, TASK_ON_RQ_MIGRATING, task_on_rq_migrating()
> and task_on_rq_queued().
>
> I've pulled the latest version from peterz/queue.git, and Peter's changes
> are included.
>
> This series aims to get rid of some places where locks of two RQs are held
> at the same time.
>
> Patch [1/5] is a preparation/cleanup. It replaces old (task_struct::on_rq ==
> 1)
> with new (task_struct::on_rq == TASK_ON_RQ_QUEUED) everywhere. No functional
> changes.
>
> Patch [2/5] is main in the series. It introduces new TASK_ON_RQ_MIGRATING
> state and
> teaches scheduler to understand it (we need little changes in try_to_wake_up()
> and task_rq_lock() family). This will be used in the following way:
>
> (we are changing task's rq)
>
> raw_spin_lock(&src_rq->lock);
>
> p = ...; /* Some src_rq task */
>
> dequeue_task(src_rq, p, 0);
> p->on_rq = TASK_ON_RQ_MIGRATING;
> set_task_cpu(p, dst_cpu);
> raw_spin_unlock(&src_rq->lock);
>
> /*
> * Now p is dequeued, and both
> * RQ locks are unlocked, but
> * its on_rq is not zero.
> * Nobody can manipulate p
> * while it's migrating,
> * even when spinlocks are
> * unlocked.
> */
>
> raw_spin_lock(&dst_rq->lock);
> p->on_rq = TASK_ON_RQ_QUEUED;
> enqueue_task(dst_rq, p, 0);
> raw_spin_unlock(&dst_rq->lock);
>
> Patches [3,4,5/5] remove double locks and use new TASK_ON_RQ_MIGRATING state.
> They allow unlocked using of 3-4 function, which looks safe for me.
>
> The profit is that double_rq_lock() is not need in several places. We reduce
> the total time when RQs are locked.
>
> ---
>
> Kirill Tkhai (5):
> sched: Wrapper for checking task_struct::on_rq
> sched: Teach scheduler to understand TASK_ON_RQ_MIGRATING state
> sched: Remove double_rq_lock() from __migrate_task()
> sched/fair: Remove double_lock_balance() from
> active_load_balance_cpu_stop()
> sched/fair: Remove double_lock_balance() from load_balance()
>
>
> kernel/sched/core.c | 113 +++++++++++++++------------
> kernel/sched/deadline.c | 15 ++--
> kernel/sched/fair.c | 195
> ++++++++++++++++++++++++++++++++--------------
> kernel/sched/rt.c | 16 ++--
> kernel/sched/sched.h | 13 +++
> kernel/sched/stop_task.c | 2
> 6 files changed, 228 insertions(+), 126 deletions(-)
>
> --
> Signed-off-by: Kirill Tkhai <[email protected]>
Ok, looks good. I picked up this version, with a few minor
tweaks and fixes to the changelogs.
Thanks,
Ingo
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