On Thu, Apr 02, 2015 at 09:48:34PM +0200, Peter Zijlstra wrote:
> @@ -158,20 +257,20 @@ static void pv_wait_head(struct qspinloc
> void __pv_queue_spin_unlock(struct qspinlock *lock)
> {
> struct __qspinlock *l = (void *)lock;
> + struct pv_hash_bucket *hb;
>
> if (xchg(&l->lock
On 04/02/2015 03:48 PM, Peter Zijlstra wrote:
On Thu, Apr 02, 2015 at 07:20:57PM +0200, Peter Zijlstra wrote:
pv_wait_head():
pv_hash()
/* MB as per cmpxchg */
cmpxchg(&l->locked, _Q_LOCKED_VAL, _Q_SLOW_VAL);
VS
__pv_queue_spin_unlock():
if (xchg(&l->locked, 0
On Thu, Apr 02, 2015 at 07:20:57PM +0200, Peter Zijlstra wrote:
> pv_wait_head():
>
> pv_hash()
> /* MB as per cmpxchg */
> cmpxchg(&l->locked, _Q_LOCKED_VAL, _Q_SLOW_VAL);
>
> VS
>
> __pv_queue_spin_unlock():
>
> if (xchg(&l->locked, 0) != _Q_SLOW_VAL)
> r
On Thu, Apr 02, 2015 at 12:28:30PM -0400, Waiman Long wrote:
> On 04/01/2015 05:03 PM, Peter Zijlstra wrote:
> >On Wed, Apr 01, 2015 at 03:58:58PM -0400, Waiman Long wrote:
> >>On 04/01/2015 02:48 PM, Peter Zijlstra wrote:
> >>I am sorry that I don't quite get what you mean here. My point is that i
On 04/01/2015 05:03 PM, Peter Zijlstra wrote:
On Wed, Apr 01, 2015 at 03:58:58PM -0400, Waiman Long wrote:
On 04/01/2015 02:48 PM, Peter Zijlstra wrote:
I am sorry that I don't quite get what you mean here. My point is that in
the hashing step, a cpu will need to scan an empty bucket to put the
On Wed, Apr 01, 2015 at 03:58:58PM -0400, Waiman Long wrote:
> On 04/01/2015 02:48 PM, Peter Zijlstra wrote:
> I am sorry that I don't quite get what you mean here. My point is that in
> the hashing step, a cpu will need to scan an empty bucket to put the lock
> in. In the interim, an previously u
On 04/01/2015 01:12 PM, Peter Zijlstra wrote:
On Wed, Apr 01, 2015 at 12:20:30PM -0400, Waiman Long wrote:
After more careful reading, I think the assumption that the presence of an
unused bucket means there is no match is not true. Consider the scenario:
1. cpu 0 puts lock1 into hb[0]
2. cpu 1
On 04/01/2015 02:48 PM, Peter Zijlstra wrote:
On Wed, Apr 01, 2015 at 02:54:45PM -0400, Waiman Long wrote:
On 04/01/2015 02:17 PM, Peter Zijlstra wrote:
On Wed, Apr 01, 2015 at 07:42:39PM +0200, Peter Zijlstra wrote:
Hohumm.. time to think more I think ;-)
So bear with me, I've not really pon
On Wed, Apr 01, 2015 at 02:54:45PM -0400, Waiman Long wrote:
> On 04/01/2015 02:17 PM, Peter Zijlstra wrote:
> >On Wed, Apr 01, 2015 at 07:42:39PM +0200, Peter Zijlstra wrote:
> >>>Hohumm.. time to think more I think ;-)
> >>So bear with me, I've not really pondered this well so it could be full
>
On 04/01/2015 02:17 PM, Peter Zijlstra wrote:
On Wed, Apr 01, 2015 at 07:42:39PM +0200, Peter Zijlstra wrote:
Hohumm.. time to think more I think ;-)
So bear with me, I've not really pondered this well so it could be full
of holes (again).
After the cmpxchg(&l->locked, _Q_LOCKED_VAL, _Q_SLOW_V
On Wed, Apr 01, 2015 at 07:42:39PM +0200, Peter Zijlstra wrote:
> > Hohumm.. time to think more I think ;-)
>
> So bear with me, I've not really pondered this well so it could be full
> of holes (again).
>
> After the cmpxchg(&l->locked, _Q_LOCKED_VAL, _Q_SLOW_VAL) succeeds the
> spin_unlock() mu
On Wed, Apr 01, 2015 at 07:12:23PM +0200, Peter Zijlstra wrote:
> On Wed, Apr 01, 2015 at 12:20:30PM -0400, Waiman Long wrote:
> > After more careful reading, I think the assumption that the presence of an
> > unused bucket means there is no match is not true. Consider the scenario:
> >
> > 1. cpu
On Wed, Apr 01, 2015 at 12:20:30PM -0400, Waiman Long wrote:
> After more careful reading, I think the assumption that the presence of an
> unused bucket means there is no match is not true. Consider the scenario:
>
> 1. cpu 0 puts lock1 into hb[0]
> 2. cpu 1 puts lock2 into hb[1]
> 3. cpu 2 clear
On 03/19/2015 08:25 AM, Peter Zijlstra wrote:
On Thu, Mar 19, 2015 at 11:12:42AM +0100, Peter Zijlstra wrote:
So I was now thinking of hashing the lock pointer; let me go and quickly
put something together.
A little something like so; ideally we'd allocate the hashtable since
NR_CPUS is kinda b
On 03/19/2015 08:25 AM, Peter Zijlstra wrote:
On Thu, Mar 19, 2015 at 11:12:42AM +0100, Peter Zijlstra wrote:
So I was now thinking of hashing the lock pointer; let me go and quickly
put something together.
A little something like so; ideally we'd allocate the hashtable since
NR_CPUS is kinda b
On Thu, Mar 19, 2015 at 01:25:36PM +0100, Peter Zijlstra wrote:
> +static struct qspinlock **pv_hash(struct qspinlock *lock)
> +{
> + u32 hash = hash_ptr(lock, PV_LOCK_HASH_BITS);
> + struct pv_hash_bucket *hb, *end;
> +
> + if (!hash)
> + hash = 1;
> +
> + hb = &__pv_lo
On Thu, Mar 19, 2015 at 11:12:42AM +0100, Peter Zijlstra wrote:
> So I was now thinking of hashing the lock pointer; let me go and quickly
> put something together.
A little something like so; ideally we'd allocate the hashtable since
NR_CPUS is kinda bloated, but it shows the idea I think.
And w
On Wed, Mar 18, 2015 at 04:50:37PM -0400, Waiman Long wrote:
> >+this_cpu_write(__pv_lock_wait, lock);
>
> We may run into the same problem of needing to have 4 queue nodes per CPU.
> If an interrupt happens just after the write and before the actual wait and
> it goes through the same
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