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    SubjectRe: [PATCHv5 2/2] memory barrier: adding smp_mb__after_lock

    * Jiri Olsa <jolsa@redhat.com> wrote:

    > On Fri, Jul 03, 2009 at 11:24:38AM +0200, Ingo Molnar wrote:
    > >
    > > * Eric Dumazet <eric.dumazet@gmail.com> wrote:
    > >
    > > > Ingo Molnar a écrit :
    > > > > * Jiri Olsa <jolsa@redhat.com> wrote:
    > > > >
    > > > >> +++ b/arch/x86/include/asm/spinlock.h
    > > > >> @@ -302,4 +302,7 @@ static inline void __raw_write_unlock(raw_rwlock_t *rw)
    > > > >> #define _raw_read_relax(lock) cpu_relax()
    > > > >> #define _raw_write_relax(lock) cpu_relax()
    > > > >>
    > > > >> +/* The {read|write|spin}_lock() on x86 are full memory barriers. */
    > > > >> +#define smp_mb__after_lock() do { } while (0)
    > > > >
    > > > > Two small stylistic comments, please make this an inline function:
    > > > >
    > > > > static inline void smp_mb__after_lock(void) { }
    > > > > #define smp_mb__after_lock
    > > > >
    > > > > (untested)
    > > > >
    > > > >> +/* The lock does not imply full memory barrier. */
    > > > >> +#ifndef smp_mb__after_lock
    > > > >> +#define smp_mb__after_lock() smp_mb()
    > > > >> +#endif
    > > > >
    > > > > ditto.
    > > > >
    > > > > Ingo
    > > >
    > > > This was following existing implementations of various smp_mb__??? helpers :
    > > >
    > > > # grep -4 smp_mb__before_clear_bit include/asm-generic/bitops.h
    > > >
    > > > /*
    > > > * clear_bit may not imply a memory barrier
    > > > */
    > > > #ifndef smp_mb__before_clear_bit
    > > > #define smp_mb__before_clear_bit() smp_mb()
    > > > #define smp_mb__after_clear_bit() smp_mb()
    > > > #endif
    > >
    > > Did i mention that those should be fixed too? :-)
    > >
    > > Ingo
    >
    > ok, could I include it in the 2/2 or you prefer separate patch?

    depends on whether it will regress ;-)

    If it regresses, it's better to have it separate. If it wont, it can
    be included. If unsure, default to the more conservative option.

    Ingo
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