From: Konstantin Ananyev <konstantin.ananyev@huawei.com>
To: Bruce Richardson <bruce.richardson@intel.com>,
Thomas Monjalon <thomas@monjalon.net>
Cc: "Morten Brørup" <mb@smartsharesystems.com>,
"andrew.rybchenko@oktetlabs.ru" <andrew.rybchenko@oktetlabs.ru>,
"olivier.matz@6wind.com" <olivier.matz@6wind.com>,
"david.marchand@redhat.com" <david.marchand@redhat.com>,
"dev@dpdk.org" <dev@dpdk.org>,
"hofors@lysator.liu.se" <hofors@lysator.liu.se>,
"mattias.ronnblom@ericsson.com" <mattias.ronnblom@ericsson.com>,
"stephen@networkplumber.org" <stephen@networkplumber.org>,
"jerinj@marvell.com" <jerinj@marvell.com>
Subject: RE: FW: [PATCH v4 3/3] mempool: use cache for frequently updated stats
Date: Tue, 8 Nov 2022 17:38:04 +0000 [thread overview]
Message-ID: <74775cadd8174c3797b4076929ebbcb7@huawei.com> (raw)
In-Reply-To: <Y2p82O/EUF/NziJR@bricha3-MOBL.ger.corp.intel.com>
>
> On Tue, Nov 08, 2022 at 04:51:11PM +0100, Thomas Monjalon wrote:
> > 08/11/2022 15:30, Morten Brørup:
> > > > From: Thomas Monjalon [mailto:thomas@monjalon.net]
> > > > 08/11/2022 12:25, Morten Brørup:
> > > > > From: Morten Brørup
> > > > > > From: Konstantin Ananyev [mailto:konstantin.ananyev@huawei.com]
> > > > > > Sent: Tuesday, 8 November 2022 10.20
> > > > > > > +#ifdef RTE_LIBRTE_MEMPOOL_STATS
> > > > > > > +#define RTE_MEMPOOL_CACHE_STAT_ADD(cache, name, n) (cache)-
> > > > >stats.name += n
> > > > > >
> > > > > > As Andrew already pointed, it needs to be: ((cache)->stats.name +=
> > > > (n))
> > > > > > Apart from that, LGTM.
> > > > > > Series-Acked-by: Konstantin Ananyev <konstantin.ananyev@huawei.com>
> > > > >
> > > > > @Thomas, this series should be ready to apply... it now has been:
> > > > > Reviewed-by: (mempool maintainer) Andrew Rybchenko
> > > > <andrew.rybchenko@oktetlabs.ru>
> > > > > Reviewed-By: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> > > > > Acked-by: Konstantin Ananyev <konstantin.ananyev@huawei.com>
> > > >
> > > > Being acked does not mean it is good to apply in -rc3.
> > >
> > > I understand that the RFC/v1 of this series was formally too late to make it in 22.11, so I will not complain loudly if you choose to
> omit it for 22.11.
> > >
> > > With two independent reviews, including from a mempool maintainer, I still have some hope. Also considering the risk assessment
> below. ;-)
> > >
> > > > Please tell what is the benefit for 22.11 (before/after and condition).
> > >
> > > Short version: With this series, mempool statistics can be used in production. Without it, the performance cost
> (mempool_perf_autotest: -74 %) is prohibitive!
> > >
> > > Long version:
> > >
> > > The patch series provides significantly higher performance for mempool statistics, which are readable through
> rte_mempool_dump(FILE *f, struct rte_mempool *mp).
> > >
> > > Without this series, you have to set RTE_LIBRTE_MEMPOOL_DEBUG at build time to get mempool statistics.
> RTE_LIBRTE_MEMPOOL_DEBUG also enables protective cookies before and after each mempool object, which are all verified on
> get/put from the mempool. According to mempool_perf_autotest, the performance cost of mempool statistics (by setting
> RTE_LIBRTE_MEMPOOL_DEBUG) is a 74 % decrease in rate_persec for mempools with cache (i.e. mbuf pools). Prohibitive for use in
> production!
> > >
> > > With this series, the performance cost of mempool statistics (by setting RTE_LIBRTE_MEMPOOL_STATS) in
> mempool_perf_autotest is only 6.7 %, so mempool statistics can be used in production.
> > >
> > > > Note there is a real risk doing such change that late.
> > >
> > > Risk assessment:
> > >
> > > The patch series has zero effect unless either RTE_LIBRTE_MEMPOOL_DEBUG or RTE_LIBRTE_MEMPOOL_STATS are set when
> building. They are not set in the default build.
> >
> > If theses build flags are not set, there is no risk and no benefit.
> > But if they are set, there is a risk of regression,
> > for the benefit of an increased performance of a debug feature.
> > I would say it is better to avoid any functional regression in a debug feature
> > at this stage.
> > Any other opinion?
> >
> While I agree that we should avoid any functional regression, I wonder how
> widely used the debug feature is, and how big the risk of a regression is?
> Even if there is one, having a regression in a debug feature is a lot less
> serious than having one in something which goes into production.
>
Unless it introduces an ABI breakage (as I understand it doesn't), I'll wait till 23.03.
Just in case.
BTW, as a side thought - if the impact is really that small now, would it make sense to make
it run-time option, instead of compile-time one?
Konstantin
next prev parent reply other threads:[~2022-11-08 17:38 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-08 11:25 Morten Brørup
2022-11-08 13:32 ` Thomas Monjalon
2022-11-08 14:30 ` Morten Brørup
2022-11-08 15:51 ` Thomas Monjalon
2022-11-08 15:59 ` Bruce Richardson
2022-11-08 17:38 ` Konstantin Ananyev [this message]
2022-11-09 5:03 ` Morten Brørup
2022-11-09 8:21 ` Mattias Rönnblom
2022-11-09 10:19 ` Konstantin Ananyev
2022-11-09 11:42 ` Morten Brørup
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