On Fri, Apr 01, 2016 at 01:43:03PM +0200, Peter Zijlstra wrote:
> > Ah, yes, I forgot about that. Lemme go find that discussions and see
> > what I can do there.
>
> Completely untested..
>
> ---
> include/linux/compiler.h | 20 ++++++++++++++------
> kernel/locking/qspinlock.c | 12 ++++++------
> kernel/sched/core.c | 9 +++++----
> kernel/sched/sched.h | 2 +-
> kernel/smp.c | 2 +-
> 5 files changed, 27 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index b5ff9881bef8..c64f5897664f 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -305,7 +305,8 @@ static __always_inline void __write_once_size(volatile
> void *p, void *res, int s
> })
>
> /**
> - * smp_cond_acquire() - Spin wait for cond with ACQUIRE ordering
> + * smp_cond_load_acquire() - Spin wait for cond with ACQUIRE ordering
> + * @ptr: pointer to the variable wait on
> * @cond: boolean expression to wait for
> *
> * Equivalent to using smp_load_acquire() on the condition variable but
> employs
> @@ -315,11 +316,18 @@ static __always_inline void __write_once_size(volatile
> void *p, void *res, int s
> * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,
> * aka. ACQUIRE.
> */
> -#define smp_cond_acquire(cond) do { \
> - while (!(cond)) \
> - cpu_relax(); \
> - smp_rmb(); /* ctrl + rmb := acquire */ \
> -} while (0)
> +#define smp_cond_load_acquire(ptr, cond_expr) ({ \
> + typeof(ptr) __PTR = (ptr); \
> + typeof(*ptr) VAL; \
It's a bit grim having a magic variable name, but I have no better
suggestion.
> + for (;;) { \
> + VAL = READ_ONCE(*__PTR); \
> + if (cond_expr) \
> + break; \
> + cpu_relax(); \
> + } \
> + smp_rmb(); /* ctrl + rmb := acquire */ \
> + VAL; \
> +})
Can you stick some #ifndef guards around this, please? That way I can do
my ldxr/wfe-based version for ARM that makes the spinning tolerable. Also,
wouldn't this be better suited to barrier.h?
Otherwise, I really like this idea. Thanks!
Will
