From: "Morten Brørup" <mb@smartsharesystems.com>
To: "Andrew Rybchenko" <andrew.rybchenko@oktetlabs.ru>,
<olivier.matz@6wind.com>, <dev@dpdk.org>
Cc: <honnappa.nagarahalli@arm.com>, <bruce.richardson@intel.com>,
<konstantin.ananyev@huawei.com>
Subject: RE: [PATCH] mempool: micro-optimize put function
Date: Wed, 16 Nov 2022 12:10:21 +0100 [thread overview]
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35D874C7@smartserver.smartshare.dk> (raw)
In-Reply-To: <cc8ddab3-f8ed-1a57-ace8-bdcb06fad75f@oktetlabs.ru>
> From: Andrew Rybchenko [mailto:andrew.rybchenko@oktetlabs.ru]
> Sent: Wednesday, 16 November 2022 12.05
>
> On 11/16/22 13:18, Morten Brørup wrote:
> > Micro-optimization:
> > Reduced the most likely code path in the generic put function by
> moving an
> > unlikely check out of the most likely code path and further down.
> >
> > Also updated the comments in the function.
> >
> > Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
> > ---
> > lib/mempool/rte_mempool.h | 35 ++++++++++++++++++-----------------
> > 1 file changed, 18 insertions(+), 17 deletions(-)
> >
> > diff --git a/lib/mempool/rte_mempool.h b/lib/mempool/rte_mempool.h
> > index 9f530db24b..aba90dbb5b 100644
> > --- a/lib/mempool/rte_mempool.h
> > +++ b/lib/mempool/rte_mempool.h
> > @@ -1364,32 +1364,33 @@ rte_mempool_do_generic_put(struct rte_mempool
> *mp, void * const *obj_table,
> > {
> > void **cache_objs;
> >
> > - /* No cache provided */
> > + /* No cache provided? */
> > if (unlikely(cache == NULL))
> > goto driver_enqueue;
> >
> > - /* increment stat now, adding in mempool always success */
> > + /* Increment stats now, adding in mempool always succeeds. */
> > RTE_MEMPOOL_CACHE_STAT_ADD(cache, put_bulk, 1);
> > RTE_MEMPOOL_CACHE_STAT_ADD(cache, put_objs, n);
> >
> > - /* The request itself is too big for the cache */
> > - if (unlikely(n > cache->flushthresh))
> > - goto driver_enqueue_stats_incremented;
>
> I've kept the check here since it protects against overflow in len plus
> n below if n is really huge.
We can fix that, see below.
>
> > -
> > - /*
> > - * The cache follows the following algorithm:
> > - * 1. If the objects cannot be added to the cache without
> crossing
> > - * the flush threshold, flush the cache to the backend.
> > - * 2. Add the objects to the cache.
> > - */
> > -
> > - if (cache->len + n <= cache->flushthresh) {
> > + if (likely(cache->len + n <= cache->flushthresh)) {
It is an invariant that cache->len <= cache->flushthresh, so the above comparison can be rewritten to protect against overflow:
if (likely(n <= cache->flushthresh - cache->len)) {
> > + /*
> > + * The objects can be added to the cache without crossing
> the
> > + * flush threshold.
> > + */
> > cache_objs = &cache->objs[cache->len];
> > cache->len += n;
> > - } else {
> > + } else if (likely(n <= cache->flushthresh)) {
> > + /*
> > + * The request itself fits into the cache.
> > + * But first, the cache must be flushed to the backend, so
> > + * adding the objects does not cross the flush threshold.
> > + */
> > cache_objs = &cache->objs[0];
> > rte_mempool_ops_enqueue_bulk(mp, cache_objs, cache->len);
> > cache->len = n;
> > + } else {
> > + /* The request itself is too big for the cache. */
> > + goto driver_enqueue_stats_incremented;
> > }
> >
> > /* Add the objects to the cache. */
> > @@ -1399,13 +1400,13 @@ rte_mempool_do_generic_put(struct rte_mempool
> *mp, void * const *obj_table,
> >
> > driver_enqueue:
> >
> > - /* increment stat now, adding in mempool always success */
> > + /* Increment stats now, adding in mempool always succeeds. */
> > RTE_MEMPOOL_STAT_ADD(mp, put_bulk, 1);
> > RTE_MEMPOOL_STAT_ADD(mp, put_objs, n);
> >
> > driver_enqueue_stats_incremented:
> >
> > - /* push objects to the backend */
> > + /* Push the objects to the backend. */
> > rte_mempool_ops_enqueue_bulk(mp, obj_table, n);
> > }
> >
>
next prev parent reply other threads:[~2022-11-16 11:10 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-16 10:18 Morten Brørup
2022-11-16 11:04 ` Andrew Rybchenko
2022-11-16 11:10 ` Morten Brørup [this message]
2022-11-16 11:29 ` Andrew Rybchenko
2022-11-16 12:14 ` [PATCH v2] " Morten Brørup
2022-11-16 15:51 ` Honnappa Nagarahalli
2022-11-16 15:59 ` Morten Brørup
2022-11-16 16:26 ` Honnappa Nagarahalli
2022-11-16 17:39 ` Morten Brørup
2022-12-19 8:50 ` Morten Brørup
2022-12-22 13:52 ` Konstantin Ananyev
2022-12-22 15:02 ` Morten Brørup
2022-12-23 16:34 ` Konstantin Ananyev
2022-12-24 10:46 ` [PATCH v3] " Morten Brørup
2022-12-27 8:54 ` Andrew Rybchenko
2022-12-27 15:37 ` Morten Brørup
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=98CBD80474FA8B44BF855DF32C47DC35D874C7@smartserver.smartshare.dk \
--to=mb@smartsharesystems.com \
--cc=andrew.rybchenko@oktetlabs.ru \
--cc=bruce.richardson@intel.com \
--cc=dev@dpdk.org \
--cc=honnappa.nagarahalli@arm.com \
--cc=konstantin.ananyev@huawei.com \
--cc=olivier.matz@6wind.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).