From: Tyler Retzlaff <roretzla@linux.microsoft.com>
To: "Morten Brørup" <mb@smartsharesystems.com>
Cc: Bruce Richardson <bruce.richardson@intel.com>,
olivier.matz@6wind.com, andrew.rybchenko@oktetlabs.ru,
dev@dpdk.org
Subject: Re: [PATCH] mempool: optimize get objects with constant n
Date: Tue, 18 Apr 2023 09:01:59 -0700 [thread overview]
Message-ID: <20230418160159.GB4574@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> (raw)
In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35D87892@smartserver.smartshare.dk>
On Tue, Apr 18, 2023 at 05:50:56PM +0200, Morten Brørup wrote:
> > From: Tyler Retzlaff [mailto:roretzla@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:roretzla@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 <mb@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.richardson@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.
yeah, no kidding. i wish the process was a bit more friendly being on
the receiving end. it's unfortunate because it is discouraging
improvements.
i'll bring a patch for it then.
next prev parent reply other threads:[~2023-04-18 16:02 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-11 6:48 Morten Brørup
2023-04-18 11:06 ` Bruce Richardson
2023-04-18 11:29 ` Morten Brørup
2023-04-18 12:54 ` Bruce Richardson
2023-04-18 12:55 ` Bruce Richardson
2023-06-07 7:51 ` Thomas Monjalon
2023-06-07 8:03 ` Morten Brørup
2023-06-07 8:10 ` Thomas Monjalon
2023-06-07 8:33 ` Morten Brørup
2023-06-07 8:41 ` Morten Brørup
2023-04-18 15:15 ` Tyler Retzlaff
2023-04-18 15:30 ` Morten Brørup
2023-04-18 15:44 ` Tyler Retzlaff
2023-04-18 15:50 ` Morten Brørup
2023-04-18 16:01 ` Tyler Retzlaff [this message]
2023-04-18 16:05 ` Morten Brørup
2023-04-18 19:51 ` [PATCH v3] " Morten Brørup
2023-04-18 20:09 ` [PATCH v4] " Morten Brørup
2023-06-07 9:12 ` Thomas Monjalon
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