Re: [dpdk-dev] [PATCH v2 1/2] spinlock: use wfe to reduce contention on aarch64

[Jerin Jacob <jerinjacobk@gmail.com>]

On Sun, Apr 26, 2020 at 2:09 PM Gavin Hu <gavin.hu@arm.com> wrote:
>
> In acquiring a spinlock, cores repeatedly poll the lock variable.
> This is replaced by rte_wait_until_equal API.
>
> Running the micro benchmarking and the testpmd and l3fwd traffic tests
> on ThunderX2, Ampere eMAG80 and Arm N1SDP, everything went well and no
> notable performance gain nor degradation was measured.
>
> Signed-off-by: Gavin Hu <gavin.hu@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> Reviewed-by: Phil Yang <phil.yang@arm.com>
> Reviewed-by: Steve Capper <steve.capper@arm.com>
> Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>
> Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> Tested-by: Pavan Nikhilesh <pbhagavatula@marvell.com>

Acked-by: Jerin Jacob <jerinj@marvell.com>


> ---
>  lib/librte_eal/include/generic/rte_spinlock.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/lib/librte_eal/include/generic/rte_spinlock.h b/lib/librte_eal/include/generic/rte_spinlock.h
> index 87ae7a4f1..40fe49d5a 100644
> --- a/lib/librte_eal/include/generic/rte_spinlock.h
> +++ b/lib/librte_eal/include/generic/rte_spinlock.h
> @@ -65,8 +65,8 @@ rte_spinlock_lock(rte_spinlock_t *sl)
>
>         while (!__atomic_compare_exchange_n(&sl->locked, &exp, 1, 0,
>                                 __ATOMIC_ACQUIRE, __ATOMIC_RELAXED)) {
> -               while (__atomic_load_n(&sl->locked, __ATOMIC_RELAXED))
> -                       rte_pause();
> +               rte_wait_until_equal_32((volatile uint32_t *)&sl->locked,
> +                              0, __ATOMIC_RELAXED);
>                 exp = 0;
>         }
>  }
> --
> 2.17.1
>