Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 11 Jun 2013 10:52:53 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC ticketlock] v2 Auto-queued ticketlock |
| |
On Tue, Jun 11, 2013 at 01:36:27PM -0400, Steven Rostedt wrote: > On Tue, 2013-06-11 at 10:02 -0700, Paul E. McKenney wrote: > > > +#ifdef CONFIG_TICKET_LOCK_QUEUED > > + > > +#define __TKT_SPIN_INC 2 > > +bool tkt_spin_pass(arch_spinlock_t *ap, struct __raw_tickets inc); > > + > > +#else /* #ifdef CONFIG_TICKET_LOCK_QUEUED */ > > + > > +#define __TKT_SPIN_INC 1 > > +static inline bool tkt_spin_pass(arch_spinlock_t *ap, struct __raw_tickets inc) > > +{ > > + return false; > > +} > > + > > +#endif /* #else #ifdef CONFIG_TICKET_LOCK_QUEUED */ > > + > > /* > > * Ticket locks are conceptually two parts, one indicating the current head of > > * the queue, and the other indicating the current tail. The lock is acquired > > @@ -49,17 +64,15 @@ > > */ > > static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock) > > { > > - register struct __raw_tickets inc = { .tail = 1 }; > > + register struct __raw_tickets inc = { .tail = __TKT_SPIN_INC }; > > > > inc = xadd(&lock->tickets, inc); > > - > > for (;;) { > > - if (inc.head == inc.tail) > > + if (inc.head == inc.tail || tkt_spin_pass(lock, inc)) > > break; > > - cpu_relax(); > > Overheating the CPU are we ;-) > > Keeping the cpu_relax() doesn't hurt, even when TICKET_LOCK_QUEUE is > enabled. As the only latency to worry about is when tkt_spin_pass() > returns true, where it breaks out of the loop anyway. > > But if you really don't want the double call to cpu_relax(), we can > probably remove the cpu_relax from tkt_spin_pass() and keep this one, or > in the above tkt_spin_pass() where TICK_LOCK_QUEUED is not set, we can > do: > > static inline bool tkt_spin_pass(arch_spinlock_t *ap, struct > __raw_tickets inc) > { > cpu_relax(); > return false; > } > > Honesty, I would say remove it from tkt_spin_pass() when returning > false.
Sold! I moved the cpu_relax() from tkt_spin_pass()'s false return to the spin loop in __ticket_spin_lock(). Misguided attempt on my part to minimize __ticket_spin_lock()'s size.
Thanx, Paul
> -- Steve > > > > inc.head = ACCESS_ONCE(lock->tickets.head); > > } > > - barrier(); /* make sure nothing creeps before the lock is taken */ > > + barrier(); /* Make sure nothing creeps in before the lock is taken. */ > > } > > > >
| ![\](/images/icornerr.gif) |