On 2023-05-12 13:59, Jerin Jacob wrote: > On Thu, May 11, 2023 at 2:00 PM Mattias Rönnblom > <mattias.ronnb...@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.ronnb...@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.
The __builtin_constant_p() is introduced to avoid having the compiler generate a conditional branch and two different code paths in case nb_elem is a run-time variable. In particular, this matters if nb_elems is run-time variable and varies between 1 and some larger value. I should have mention this in the commit message. A very slight performance improvement. It also makes the code better match the comment, imo. Zero cost for const one enqueues, but no impact non-compile-time-constant-length enqueues. Feel free to ignore. > 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 >>
