Re: [PATCH v3] eventdev: avoid non-burst shortcut for variable-size bursts

[Jerin Jacob <jerinjacobk@gmail.com>]

On Thu, May 11, 2023 at 2:00 PM Mattias Rönnblom
<mattias.ronnblom@ericsson.com> wrote:
>
> Use non-burst event enqueue and dequeue calls from burst enqueue and
> dequeue only when the burst size is compile-time constant (and equal
> to one).
>
> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
>
> ---
>
> v3: Actually include the change v2 claimed to contain.
> v2: Wrap builtin call in __extension__, to avoid compiler warnings if
>     application is compiled with -pedantic. (Morten Brørup)
> ---
>  lib/eventdev/rte_eventdev.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/lib/eventdev/rte_eventdev.h b/lib/eventdev/rte_eventdev.h
> index a90e23ac8b..a471caeb6d 100644
> --- a/lib/eventdev/rte_eventdev.h
> +++ b/lib/eventdev/rte_eventdev.h
> @@ -1944,7 +1944,7 @@ __rte_event_enqueue_burst(uint8_t dev_id, uint8_t port_id,
>          * Allow zero cost non burst mode routine invocation if application
>          * requests nb_events as const one
>          */
> -       if (nb_events == 1)
> +       if (__extension__(__builtin_constant_p(nb_events)) && nb_events == 1)

"Why" part is not clear from the commit message. Is this to avoid
nb_events read if it is built-in const.
If so, check should be following. Right?

if (__extension__((__builtin_constant_p(nb_events)) && nb_events == 1)
|| nb_events  == 1)

At least, It was my original intention in the code.



>                 return (fp_ops->enqueue)(port, ev);
>         else
>                 return fn(port, ev, nb_events);
> @@ -2200,7 +2200,7 @@ rte_event_dequeue_burst(uint8_t dev_id, uint8_t port_id, struct rte_event ev[],
>          * Allow zero cost non burst mode routine invocation if application
>          * requests nb_events as const one
>          */
> -       if (nb_events == 1)
> +       if (__extension__(__builtin_constant_p(nb_events)) && nb_events == 1)
>                 return (fp_ops->dequeue)(port, ev, timeout_ticks);
>         else
>                 return (fp_ops->dequeue_burst)(port, ev, nb_events,
> --
> 2.34.1
>