From: "Wang, Xiao W" <xiao.w.wang@intel.com>
To: Olivier Matz <olivier.matz@6wind.com>,
Andrew Rybchenko <arybchenko@solarflare.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] mempool: optimize copy in cache get
Date: Mon, 1 Jul 2019 14:21:41 +0000 [thread overview]
Message-ID: <B7F2E978279D1D49A3034B7786DACF407AF5B530@SHSMSX106.ccr.corp.intel.com> (raw)
In-Reply-To: <20190701131103.zi72h3me63mzg73v@platinum>
Hi,
> -----Original Message-----
> From: Olivier Matz [mailto:olivier.matz@6wind.com]
> Sent: Monday, July 1, 2019 9:11 PM
> To: Andrew Rybchenko <arybchenko@solarflare.com>
> Cc: Wang, Xiao W <xiao.w.wang@intel.com>; dev@dpdk.org
> Subject: Re: [PATCH] mempool: optimize copy in cache get
>
> Hi,
>
> On Tue, May 21, 2019 at 12:34:55PM +0300, Andrew Rybchenko wrote:
> > On 5/21/19 12:03 PM, Xiao Wang wrote:
> > > Use rte_memcpy to improve the pointer array copy. This optimization
> method
> > > has already been applied to __mempool_generic_put() [1], this patch
> applies
> > > it to __mempool_generic_get(). Slight performance gain can be observed
> in
> > > testpmd txonly test.
> > >
> > > [1] 863bfb47449 ("mempool: optimize copy in cache")
> > >
> > > Signed-off-by: Xiao Wang <xiao.w.wang@intel.com>
> > > ---
> > > lib/librte_mempool/rte_mempool.h | 7 +------
> > > 1 file changed, 1 insertion(+), 6 deletions(-)
> > >
> > > diff --git a/lib/librte_mempool/rte_mempool.h
> b/lib/librte_mempool/rte_mempool.h
> > > index 8053f7a04..975da8d22 100644
> > > --- a/lib/librte_mempool/rte_mempool.h
> > > +++ b/lib/librte_mempool/rte_mempool.h
> > > @@ -1344,15 +1344,11 @@ __mempool_generic_get(struct
> rte_mempool *mp, void **obj_table,
> > > unsigned int n, struct rte_mempool_cache *cache)
> > > {
> > > int ret;
> > > - uint32_t index, len;
> > > - void **cache_objs;
> > > /* No cache provided or cannot be satisfied from cache */
> > > if (unlikely(cache == NULL || n >= cache->size))
> > > goto ring_dequeue;
> > > - cache_objs = cache->objs;
> > > -
> > > /* Can this be satisfied from the cache? */
> > > if (cache->len < n) {
> > > /* No. Backfill the cache first, and then fill from it */
> > > @@ -1375,8 +1371,7 @@ __mempool_generic_get(struct rte_mempool
> *mp, void **obj_table,
> > > }
> > > /* Now fill in the response ... */
> > > - for (index = 0, len = cache->len - 1; index < n; ++index, len--,
> obj_table++)
> > > - *obj_table = cache_objs[len];
> > > + rte_memcpy(obj_table, &cache->objs[cache->len - n], sizeof(void *) *
> n);
> > > cache->len -= n;
> >
> > I think the idea of the loop above is to get objects in reverse order to
> > order
> > to reuse cache top objects (put last) first. It should improve cache hit
> > etc.
> > So, performance effect of the patch could be very different on various CPUs
> > (with different cache sizes) and various work-loads.
> >
> > So, I doubt that it is a step in right direction.
>
> For reference, this was already discussed 3 years ago:
>
> https://mails.dpdk.org/archives/dev/2016-May/039873.html
> https://mails.dpdk.org/archives/dev/2016-June/040029.html
>
> I'm still not convinced that reversing object addresses (as it's done
> today) is really important. But Andrew is probably right, the impact of
> this kind of patch probably varies depending on many factors. More
> performance numbers on real-life use-cases would help to decide what to
> do.
>
> Regards,
> Olivier
I agree, and thanks for the reference link. So theoretically neither way can be
a definite best choice, it depends on various real-life factors. I'm thinking about
how to let app developer be aware of this so that they themselves could make
the choice. Or it's not worth doing due to small perf gain?
BRs,
Xiao
next prev parent reply other threads:[~2019-07-01 14:22 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-21 9:03 Xiao Wang
2019-05-21 9:34 ` Andrew Rybchenko
2019-07-01 13:11 ` Olivier Matz
2019-07-01 14:21 ` Wang, Xiao W [this message]
2019-07-01 15:00 ` Olivier Matz
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