On Fri, May 12, 2023 at 7:26 PM Morten Brørup <m...@smartsharesystems.com> wrote: > > > 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.
Yes. That was the reason for I was skipping __builtin_constant_p in the initial version.
