> From: Mattias Rönnblom [mailto:mattias.ronnb...@ericsson.com] > Sent: Friday, 12 May 2023 15.15 > > 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)
@Mattias: You missed the second part of this comparison, also catching nb_events == 1 with non-constant nb_events. @Jerin: Such a change has no effect, compared to the original code. > > > > At least, It was my original intention in the code. @Jerin: Mattias implemented exactly what the comment says. Perhaps only the comment should be updated, not the code. Is nb_events likely to be non-constant 1, and are there benefits to calling either of the non-burst functions in those cases, vs. the branch cost of this comparison (which Mattias' patch gets rid of)? > > > > > > > >> 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 > >>
