> From: Tyler Retzlaff [mailto:roret...@linux.microsoft.com] > Sent: Tuesday, 18 April 2023 17.45 > > On Tue, Apr 18, 2023 at 05:30:27PM +0200, Morten Brørup wrote: > > > From: Tyler Retzlaff [mailto:roret...@linux.microsoft.com] > > > Sent: Tuesday, 18 April 2023 17.15 > > > > > > On Tue, Apr 18, 2023 at 12:06:42PM +0100, Bruce Richardson wrote: > > > > On Tue, Apr 11, 2023 at 08:48:45AM +0200, Morten Brørup wrote: > > > > > When getting objects from the mempool, the number of objects to > get > > > is > > > > > often constant at build time. > > > > > > > > > > This patch adds another code path for this case, so the compiler > can > > > > > optimize more, e.g. unroll the copy loop when the entire request > is > > > > > satisfied from the cache. > > > > > > > > > > On an Intel(R) Xeon(R) E5-2620 v4 CPU, and compiled with gcc > 9.4.0, > > > > > mempool_perf_test with constant n shows an increase in > rate_persec > > > by an > > > > > average of 17 %, minimum 9.5 %, maximum 24 %. > > > > > > > > > > The code path where the number of objects to get is unknown at > build > > > time > > > > > remains essentially unchanged. > > > > > > > > > > Signed-off-by: Morten Brørup <m...@smartsharesystems.com> > > > > > > > > Change looks a good idea. Some suggestions inline below, which you > may > > > want to > > > > take on board for any future version. I'd strongly suggest adding > some > > > > extra clarifying code comments, as I suggest below. > > > > With those exta code comments: > > > > > > > > Acked-by: Bruce Richardson <bruce.richard...@intel.com> > > > > > > > > > --- > > > > > lib/mempool/rte_mempool.h | 24 +++++++++++++++++++++--- > > > > > 1 file changed, 21 insertions(+), 3 deletions(-) > > > > > > > > > > diff --git a/lib/mempool/rte_mempool.h > b/lib/mempool/rte_mempool.h > > > > > index 9f530db24b..ade0100ec7 100644 > > > > > --- a/lib/mempool/rte_mempool.h > > > > > +++ b/lib/mempool/rte_mempool.h > > > > > @@ -1500,15 +1500,33 @@ rte_mempool_do_generic_get(struct > > > rte_mempool *mp, void **obj_table, > > > > > if (unlikely(cache == NULL)) > > > > > goto driver_dequeue; > > > > > > > > > > - /* Use the cache as much as we have to return hot objects > first */ > > > > > - len = RTE_MIN(remaining, cache->len); > > > > > cache_objs = &cache->objs[cache->len]; > > > > > + > > > > > + if (__extension__(__builtin_constant_p(n)) && n <= cache- > >len) { > > > > > > don't take direct dependency on compiler builtins. define a macro so > we > > > don't have to play shotgun surgery later. > > > > > > also what is the purpose of using __extension__ here? are you > annotating > > > the use of __builtin_constant_p() or is there more? because if > that's > > > the only reason i see no need to use __extension__ when already > using a > > > compiler specific builtin like this, that it is not standard is > implied > > > and enforced by a compile break. > > > > ARM 32-bit memcpy() [1] does it this way, so I did the same. > > > > [1]: > https://elixir.bootlin.com/dpdk/v23.03/source/lib/eal/arm/include/rte_me > mcpy_32.h#L122 > > i see thanks. > > > > > While I agree that a macro for __builtin_constant_p() would be good, > it belongs in a patch to fix portability, not in this patch. > > i agree it isn't composite of this change. > > would you mind introducing it as a separate patch and depending on it or > do you feel that would delay this patch too much? i wouldn't mind doing > it myself but there is a long merge time on my patches which means i end > up having to carry the adaptations locally for weeks at a time.
I would rather not. Introducing global macros in rte_common.h usually triggers a lot of discussion and pushback, and I don't want it to hold back this patch.
