Messages in this thread | | | Date | Fri, 7 Feb 2014 16:43:46 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] Convert powerpc simple spinlocks into ticket locks |
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On Fri, Feb 07, 2014 at 04:18:47PM +0100, Peter Zijlstra wrote: > void ticket_lock(tickets_t *lock) > { > tickets_t t; > > /* > * Because @head is MSB, the direct increment wrap doesn't disturb > * @tail. > */ > t.pair = xadd(&lock->pair, 1<<16); > > if (likely(t.head == t.tail)) { > __lwsync(); /* acquire */ > return; > } > > while (smp_load_acquire(&lock->tail) != t.tail) > cpu_relax();
That should be "!= t.head", for that contains our ticket.
I'm hopelessly scatter brained today it seems :/
> } > > void ticket_unlock(tickets_t *lock) > { > ticket_t tail = lock->tail + 1; > > /* > * The store is save against the xadd for it will make the ll/sc fail > * and try again. Aside from that PowerISA guarantees single-copy > * atomicy for half-word writes. > * > * And since only the lock owner will ever write the tail, we're good. > */ > smp_store_release(&lock->tail, tail); > }
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