On Fri, Dec 21, 2012 at 3:50 PM, Rik van Riel <r...@redhat.com> wrote: > diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h > index 33692ea..2a45eb0 100644 > --- a/arch/x86/include/asm/spinlock.h > +++ b/arch/x86/include/asm/spinlock.h > @@ -34,6 +34,8 @@ > # define UNLOCK_LOCK_PREFIX > #endif > > +extern void ticket_spin_lock_wait(arch_spinlock_t *, struct __raw_tickets); > + > /* > * 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 > @@ -53,12 +55,11 @@ static __always_inline void > __ticket_spin_lock(arch_spinlock_t *lock) > > inc = xadd(&lock->tickets, inc); > > - for (;;) { > - if (inc.head == inc.tail) > - break; > - cpu_relax(); > - inc.head = ACCESS_ONCE(lock->tickets.head); > - } > + if (inc.head == inc.tail) > + goto out; > + > + ticket_spin_lock_wait(lock, inc); > + out:
why not just: if (inc.head != inc.tail) ticket_spin_lock_wait(lock, inc) > barrier(); /* make sure nothing creeps before the lock > is taken */ > } > > diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c > index 48d2b7d..20da354 100644 > --- a/arch/x86/kernel/smp.c > +++ b/arch/x86/kernel/smp.c > @@ -113,6 +113,20 @@ static atomic_t stopping_cpu = ATOMIC_INIT(-1); > static bool smp_no_nmi_ipi = false; > > /* > + * Wait on a congested ticket spinlock. > + */ > +void ticket_spin_lock_wait(arch_spinlock_t *lock, struct __raw_tickets inc) > +{ > + for (;;) { > + cpu_relax(); > + inc.head = ACCESS_ONCE(lock->tickets.head); > + > + if (inc.head == inc.tail) > + break; > + } Why not just: do { cpu_relax() inc.head = ... } while (inc.head != inc.tail); Other than that, no problems with the principle of it. -- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/