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 == ONRQ_QUEUED) everywhere. No functional changes.
Patch [2/5] is main in the series. It introduces new ONRQ_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 = ONRQ_MIGRATING;
set_task_cpu(p, dst_cpu);
raw_spin_unlock(&src_rq->lock);
/*
* Now p os 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 = ONRQ_QUEUED;
enqueue_task(dst_rq, p, 0);
raw_spin_unlock(&dst_rq->lock);
Patches [3,4,5/5] remove double locks and use new ONRQ_MIGRATING state.
They allow unlocked using of 3-4 function, which looks safe for me.
The profit is double_rq_lock() is not need now, so 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 ONRQ_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 | 115 +++++++++++++++++--------------
kernel/sched/deadline.c | 14 ++--
kernel/sched/fair.c | 172 +++++++++++++++++++++++++++++++---------------
kernel/sched/rt.c | 16 ++--
kernel/sched/sched.h | 13 +++
kernel/sched/stop_task.c | 2 -
6 files changed, 211 insertions(+), 121 deletions(-)
--
Signed-off-by: Kirill Tkhai <ktk...@parallels.com>
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