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Groups > linux.kernel > #1224184
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt |
| Date | 2015-09-14 16:10 +0200 |
| Message-ID | <q8CCe-8ro-21@gated-at.bofh.it> (permalink) |
| References | <q7BoS-1rn-5@gated-at.bofh.it> <q7BoS-1rn-11@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Fri, Sep 11, 2015 at 02:37:37PM -0400, Waiman Long wrote:
> This patch allows one attempt for the lock waiter to steal the lock
> when entering the PV slowpath. This helps to reduce the performance
> penalty caused by lock waiter preemption while not having much of
> the downsides of a real unfair lock.
> @@ -415,8 +458,12 @@ static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node)
>
> for (;; waitcnt++) {
> for (loop = SPIN_THRESHOLD; loop; loop--) {
> - if (!READ_ONCE(l->locked))
> - return;
> + /*
> + * Try to acquire the lock when it is free.
> + */
> + if (!READ_ONCE(l->locked) &&
> + (cmpxchg(&l->locked, 0, _Q_LOCKED_VAL) == 0))
> + goto gotlock;
> cpu_relax();
> }
>
This isn't _once_, this is once per 'wakeup'. And note that interrupts
unrelated to the kick can equally wake the vCPU up.
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[PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Waiman Long <Waiman.Long@hpe.com> - 2015-09-11 20:40 +0200
Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Peter Zijlstra <peterz@infradead.org> - 2015-09-14 16:00 +0200
Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Waiman Long <waiman.long@hpe.com> - 2015-09-14 21:10 +0200
Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Peter Zijlstra <peterz@infradead.org> - 2015-09-14 16:10 +0200
Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Waiman Long <waiman.long@hpe.com> - 2015-09-14 21:20 +0200
Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Waiman Long <waiman.long@hpe.com> - 2015-09-14 21:40 +0200
Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Peter Zijlstra <peterz@infradead.org> - 2015-09-15 10:30 +0200
Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Waiman Long <waiman.long@hpe.com> - 2015-09-15 17:30 +0200
Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Peter Zijlstra <peterz@infradead.org> - 2015-09-16 17:10 +0200
Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Waiman Long <waiman.long@hpe.com> - 2015-09-17 17:10 +0200
Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Peter Zijlstra <peterz@infradead.org> - 2015-09-14 16:10 +0200
Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Waiman Long <waiman.long@hpe.com> - 2015-09-14 21:20 +0200
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