linux-kernel - Re: [PATCH RFC ticketlock] Auto-queued ticketlock

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Date:	Mon, 10 Jun 2013 14:30:24 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...icios.com, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com, edumazet@...gle.com,
	darren@...art.com, fweisbec@...il.com, sbw@....edu,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH RFC ticketlock] Auto-queued ticketlock

On Mon, Jun 10, 2013 at 05:08:25PM -0400, Steven Rostedt wrote:
> On Sun, 2013-06-09 at 12:36 -0700, Paul E. McKenney wrote:
> >  
> > +#else /* #ifndef CONFIG_TICKET_LOCK_QUEUED */
> > +
> > +bool tkt_spin_pass(arch_spinlock_t *ap, struct __raw_tickets inc);
> > +
> > +static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
> > +{
> > +	register struct __raw_tickets inc = { .tail = 2 };
> > +
> > +	inc = xadd(&lock->tickets, inc);
> > +	for (;;) {
> > +		if (inc.head == inc.tail || tkt_spin_pass(lock, inc))
> > +			break;
> > +		inc.head = ACCESS_ONCE(lock->tickets.head);
> > +	}
> > +	barrier(); /* smp_mb() on Power or ARM. */
> > +}
> > +
> > +#endif /* #else #ifndef CONFIG_TICKET_LOCK_QUEUED */
> > +
> 
> To avoid the above code duplication, I would have this instead:

Nice!  I have updated accordingly.

							Thanx, Paul

> #ifdef CONFIG_TICKET_LOCK_QUEUED
> 
> bool tkt_spin_pass(arch_spinlock_t *ap, struct __raw_tickets inc);
> #define __TKT_SPIN_INC 2
> 
> #else
> 
> static inline bool tkt_spin_pass(arch_spinlock_t *ap, struct
> __raw_tickets inc)
> {
> 	return false;
> }
> 
> #define __TKT_SPIN_INC 1
> 
> #endif
> 
> static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
> {
> 	register struct __raw_tickets inc = { .tail = __TKT_SPIN_INC };
> 
> 	inc = xadd(&lock->tickets, inc);
> 
> 	for (;;) {
> 		if (inc.head == inc.tail || tkt_spin_pass(lock, inc))
> 			break;
> 		cpu_relax();
> 		inc.head = ACCESS_ONCE(lock->tickets.head);
> 	}
> 	barrier;	/* make sure nothing creeps before the lock is taken */
> }
> 
> -- Steve
> 
> 

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