Messages in this thread | | | Subject | [PATCH v4 0/6] sched: Add on_rq states and remove several double rq locks | From | Kirill Tkhai <> | Date | Wed, 6 Aug 2014 12:05:54 +0400 |
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This series aims to get rid of some places where locks of two RQs are held at the same time.
Patch [1/6] is a fix/preparation. It's new in v4 version of series.
Patch [2/6] 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 [3/6] 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 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 = ONRQ_QUEUED; enqueue_task(dst_rq, p, 0); raw_spin_unlock(&dst_rq->lock);
Patches [4,5,6/6] 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.
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v4: New patch [1/6]
Kirill Tkhai (6): sched/fair: Fix reschedule which is generated on throttled cfs_rq 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 | 174 +++++++++++++++++++++++++++++++--------------- kernel/sched/rt.c | 16 ++-- kernel/sched/sched.h | 13 +++ kernel/sched/stop_task.c | 2 - 6 files changed, 212 insertions(+), 122 deletions(-)
-- Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
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