Re: [dpdk-dev] [PATCH v7 3/5] eal: use wait event scheme for mcslock

[Jerin Jacob <jerinjacobk@gmail.com>]

On Thu, Oct 28, 2021 at 12:27 PM Feifei Wang <feifei.wang2@arm.com> wrote:
>
> Instead of polling for mcslock to be updated, use wait event scheme
> for this case.
>
> Furthermore, use 'uintptr_t *' is for different size of pointer in 32/64
> bits architecture.
>
> And define a new pointer 'next' for the compilation error:
> -------------------------------------------------------------------
> 'dereferencing type-punned pointer will break strict-aliasing rules'
> -------------------------------------------------------------------
>
> Signed-off-by: Feifei Wang <feifei.wang2@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> ---
>  lib/eal/include/generic/rte_mcslock.h | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/lib/eal/include/generic/rte_mcslock.h b/lib/eal/include/generic/rte_mcslock.h
> index 34f33c64a5..d5b9b293cd 100644
> --- a/lib/eal/include/generic/rte_mcslock.h
> +++ b/lib/eal/include/generic/rte_mcslock.h
> @@ -116,8 +116,9 @@ rte_mcslock_unlock(rte_mcslock_t **msl, rte_mcslock_t *me)
>                 /* More nodes added to the queue by other CPUs.
>                  * Wait until the next pointer is set.
>                  */
> -               while (__atomic_load_n(&me->next, __ATOMIC_RELAXED) == NULL)
> -                       rte_pause();
> +               uintptr_t *next = NULL;

It is going to update in the next line. Why explicit NULL assignment?

> +               next = (uintptr_t *)&me->next;
> +               rte_wait_event(next, UINTPTR_MAX, ==, 0, __ATOMIC_RELAXED);
>         }
>
>         /* Pass lock to next waiter. */
> --
> 2.25.1
>