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SubjectRe: [PATCH V3 11/27] csky: Atomic operations
Thx for the review, that's very helpful.

On Wed, Sep 12, 2018 at 05:55:14PM +0200, Peter Zijlstra wrote:
> On Wed, Sep 12, 2018 at 09:24:45PM +0800, Guo Ren wrote:
>
> > +#define ATOMIC_OP(op, c_op) \
> > +static inline void atomic_##op(int i, atomic_t *v) \
> > +{ \
> > + unsigned long tmp; \
> > + \
> > + smp_mb(); \
> > + asm volatile ( \
> > + "1: ldex.w %0, (%2) \n" \
> > + " " #op " %0, %1 \n" \
> > + " stex.w %0, (%2) \n" \
> > + " bez %0, 1b \n" \
> > + : "=&r" (tmp) \
> > + : "r" (i), "r"(&v->counter) \
> > + : "memory"); \
> > + smp_mb(); \
> > +}
>
> ATOMIC_OP doesn't need to imply any smp_mb()'s what so ever.
Ok.

> > +#define ATOMIC_OP_RETURN(op, c_op) \
> > +static inline int atomic_##op##_return(int i, atomic_t *v) \
> > +{ \
> > + unsigned long tmp, ret; \
> > + \
> > + smp_mb(); \
> > + asm volatile ( \
> > + "1: ldex.w %0, (%3) \n" \
> > + " " #op " %0, %2 \n" \
> > + " mov %1, %0 \n" \
> > + " stex.w %0, (%3) \n" \
> > + " bez %0, 1b \n" \
> > + : "=&r" (tmp), "=&r" (ret) \
> > + : "r" (i), "r"(&v->counter) \
> > + : "memory"); \
> > + smp_mb(); \
> > + \
> > + return ret; \
> > +}
> > +
> > +#define ATOMIC_FETCH_OP(op, c_op) \
> > +static inline int atomic_fetch_##op(int i, atomic_t *v) \
> > +{ \
> > + unsigned long tmp, ret; \
> > + \
> > + smp_mb(); \
> > + asm volatile ( \
> > + "1: ldex.w %0, (%3) \n" \
> > + " mov %1, %0 \n" \
> > + " " #op " %0, %2 \n" \
> > + " stex.w %0, (%3) \n" \
> > + " bez %0, 1b \n" \
> > + : "=&r" (tmp), "=&r" (ret) \
> > + : "r" (i), "r"(&v->counter) \
> > + : "memory"); \
> > + smp_mb(); \
> > + \
> > + return ret; \
> > +}
>
> For these you could generate _relaxed variants and not provide smp_mb()
> inside them.
Ok, but I'll modify it in next commit.

> > +#else /* CONFIG_CPU_HAS_LDSTEX */
> > +
> > +#include <linux/irqflags.h>
> > +
>
> > +#define ATOMIC_OP(op, c_op) \
> > +static inline void atomic_##op(int i, atomic_t *v) \
> > +{ \
> > + unsigned long tmp, flags; \
> > + \
> > + raw_local_irq_save(flags); \
> > + \
> > + asm volatile ( \
> > + " ldw %0, (%2) \n" \
> > + " " #op " %0, %1 \n" \
> > + " stw %0, (%2) \n" \
> > + : "=&r" (tmp) \
> > + : "r" (i), "r"(&v->counter) \
> > + : "memory"); \
> > + \
> > + raw_local_irq_restore(flags); \
> > +}
>
> Is this really 'better' than the generic UP fallback implementation?
There is a lock irq instruction "idly4" with out irq_save. eg:
asm volatile ( \
" idly4 \n" \
" ldw %0, (%2) \n" \
" " #op " %0, %1 \n" \
" stw %0, (%2) \n" \
I'll change to that after full tested.

> > +static inline void arch_spin_lock(arch_spinlock_t *lock)
> > +{
> > + arch_spinlock_t lockval;
> > + u32 ticket_next = 1 << TICKET_NEXT;
> > + u32 *p = &lock->lock;
> > + u32 tmp;
> > +
> > + smp_mb();
>
> spin_lock() doesn't need smp_mb() before.
read_lock and write_lock also needn't smp_mb() before, isn't it?

> > +
> > +static inline void arch_spin_unlock(arch_spinlock_t *lock)
> > +{
> > + smp_mb();
> > + lock->tickets.owner++;
> > + smp_mb();
>
> spin_unlock() doesn't need smp_mb() after.
read_unlock and write_unlock also needn't smp_mb() after, isn't it?

> > +#else /* CONFIG_QUEUED_RWLOCKS */
> > +
> > +/*
> > + * Test-and-set spin-locking.
> > + */
>
> Why retain that?
>
> same comments; it has far too many smp_mb()s in.
I'm not sure about queued_rwlocks and just for 2-cores-smp test-and-set is
faster and simpler, isn't it?

Best Regards
Guo Ren

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