Messages in this thread | | | Date | Wed, 20 Aug 2014 14:54:28 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH v5 0/5] sched: Add on_rq states and remove several double rq locks |
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* Kirill Tkhai <ktkhai@parallels.com> 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 <ktkhai@parallels.com>
Ok, looks good. I picked up this version, with a few minor tweaks and fixes to the changelogs.
Thanks,
Ingo
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