Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1224188

Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt

Show all headers | View raw

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.


> @@ -416,7 +414,8 @@ queue:
>  	 * does not imply a full barrier.
>  	 *
>  	 */

If it really were once, like the Changelog says it is, then you could
have simply added:

	if (pv_try_steal_lock(...))
		goto release;

here, and not wrecked pv_wait_head() like you did. Note that if you do
it like this, you also do not need to play games with the hash, because
you'll never get into that situation.

> -	pv_wait_head(lock, node);
> +	if (pv_wait_head_and_lock(lock, node, tail))
> +		goto release;
>  	while ((val = smp_load_acquire(&lock->val.counter)) & _Q_LOCKED_PENDING_MASK)
>  		cpu_relax();
>  
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[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

csiph-web