Messages in this thread | | | Date | Fri, 7 Feb 2014 18:55:05 +0100 | From | Torsten Duwe <> | Subject | Re: [PATCH v2] powerpc ticket locks |
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On Fri, Feb 07, 2014 at 06:12:24PM +0100, Peter Zijlstra wrote: > On Fri, Feb 07, 2014 at 05:58:01PM +0100, Torsten Duwe wrote: > > +static __always_inline void arch_spin_lock(arch_spinlock_t *lock) > > { > > + register struct __raw_tickets old, tmp, > > + inc = { .tail = TICKET_LOCK_INC }; > > + > > CLEAR_IO_SYNC; > > + __asm__ __volatile__( > > +"1: lwarx %0,0,%4 # arch_spin_lock\n" > > +" add %1,%3,%0\n" > > + PPC405_ERR77(0, "%4") > > +" stwcx. %1,0,%4\n" > > +" bne- 1b" > > + : "=&r" (old), "=&r" (tmp), "+m" (lock->tickets) > > + : "r" (inc), "r" (&lock->tickets) > > + : "cc"); > > + > > + if (likely(old.head == old.tail)) > > + goto out; > > I would have expected an lwsync someplace hereabouts.
Let me reconsider this. The v1 code worked on an 8 core, maybe I didn't beat it enough.
> > static inline void arch_spin_unlock(arch_spinlock_t *lock) > > { > > + arch_spinlock_t old, new; > > + > > +#if defined(CONFIG_PPC_SPLPAR) > > + lock->holder = 0; > > +#endif > > + do { > > + old.tickets = ACCESS_ONCE(lock->tickets); > > + new.tickets.head = old.tickets.head + TICKET_LOCK_INC; > > + new.tickets.tail = old.tickets.tail; > > + } while (unlikely(__arch_spin_cmpxchg_eq(lock, > > + old.head_tail, > > + new.head_tail))); > > SYNC_IO; > > __asm__ __volatile__("# arch_spin_unlock\n\t" > > PPC_RELEASE_BARRIER: : :"memory"); > > Doens't your cmpxchg_eq not already imply a lwsync?
Right.
> > - lock->slock = 0; > > } > > I'm still failing to see why you need an ll/sc pair for unlock.
Like so: static inline void arch_spin_unlock(arch_spinlock_t *lock) { arch_spinlock_t tmp;
#if defined(CONFIG_PPC_SPLPAR) lock->holder = 0; #endif tmp.tickets = ACCESS_ONCE(lock->tickets); tmp.tickets.head += TICKET_LOCK_INC; lock->tickets.head = tmp.tickets.head; SYNC_IO; __asm__ __volatile__("# arch_spin_unlock\n\t" PPC_RELEASE_BARRIER: : :"memory"); } ?
I'll wrap it all up next week. I only wanted to post an updated v2 with the agreed-upon changes for BenH.
Thanks so far!
Torsten
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