Messages in this thread | | | Date | Mon, 09 Nov 2015 14:53:29 -0500 | From | Waiman Long <> | Subject | Re: [PATCH tip/locking/core v9 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt |
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On 11/09/2015 12:29 PM, Peter Zijlstra wrote: > On Fri, Nov 06, 2015 at 12:47:49PM -0500, Waiman Long wrote: >> On 11/06/2015 09:50 AM, Peter Zijlstra wrote: >>> *urgh*, last time we had: >>> >>> + if (pv_wait_head_or_steal()) >>> + goto stolen; >>> while ((val = smp_load_acquire(&lock->val.counter))& _Q_LOCKED_PENDING_MASK) >>> cpu_relax(); >>> >>> ... >>> >>> +stolen: >>> while (!(next = READ_ONCE(node->next))) >>> cpu_relax(); >>> >>> ... >>> >>> Now you completely overhaul the native code.. what happened? >> I want to reuse as much of the existing native code as possible instead of >> duplicating that in the PV function. The only difference now is that the PV >> function will acquire that lock. > Right; and while I doubt it hurts the native case (you did benchmark it > I hope), I'm not too keen on the end result code wise. > > Maybe just keep the above.
I can jump over the smp_load_acquire() for PV instead of adding an additional if block. For the native code, the only thing that was added was an additional masking of val with _Q_TAIL_MASK which I don't think will make too much of a difference. > >> Semantically, I don't want to call the lock >> acquisition as lock stealing as the queue head is entitled to get the lock >> next. > Fair enough I suppose, pv_wait_head_or_lock() then? >
I am fine with that name.
>> I can rename pv_queued_spin_trylock_unfair() to >> pv_queued_spin_steal_lock() to emphasize the fact that this is the routine >> where lock stealing happens. > OK. >
Cheers, Longman
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