From: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
To: "Yang, Zhiyong" <zhiyong.yang@intel.com>,
Thomas Monjalon <thomas.monjalon@6wind.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
"yuanhan.liu@linux.intel.com" <yuanhan.liu@linux.intel.com>,
"Richardson, Bruce" <bruce.richardson@intel.com>,
"De Lara Guarch, Pablo" <pablo.de.lara.guarch@intel.com>
Subject: Re: [dpdk-dev] [PATCH 1/4] eal/common: introduce rte_memset on IA platform
Date: Thu, 8 Dec 2016 09:26:17 +0000 [thread overview]
Message-ID: <2601191342CEEE43887BDE71AB9772583F0E55B0@irsmsx105.ger.corp.intel.com> (raw)
In-Reply-To: <E182254E98A5DA4EB1E657AC7CB9BD2A3EB565EC@BGSMSX101.gar.corp.intel.com>
Hi Zhiyong,
>
> HI, Thomas:
> Sorry for late reply. I have been being always considering your suggestion.
>
> > -----Original Message-----
> > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > Sent: Friday, December 2, 2016 6:25 PM
> > To: Yang, Zhiyong <zhiyong.yang@intel.com>
> > Cc: dev@dpdk.org; yuanhan.liu@linux.intel.com; Richardson, Bruce
> > <bruce.richardson@intel.com>; Ananyev, Konstantin
> > <konstantin.ananyev@intel.com>; De Lara Guarch, Pablo
> > <pablo.de.lara.guarch@intel.com>
> > Subject: Re: [dpdk-dev] [PATCH 1/4] eal/common: introduce rte_memset on
> > IA platform
> >
> > 2016-12-05 16:26, Zhiyong Yang:
> > > +#ifndef _RTE_MEMSET_X86_64_H_
> >
> > Is this implementation specific to 64-bit?
> >
>
> Yes.
>
> > > +
> > > +#define rte_memset memset
> > > +
> > > +#else
> > > +
> > > +static void *
> > > +rte_memset(void *dst, int a, size_t n);
> > > +
> > > +#endif
> >
> > If I understand well, rte_memset (as rte_memcpy) is using the most recent
> > instructions available (and enabled) when compiling.
> > It is not adapting the instructions to the run-time CPU.
> > There is no need to downgrade at run-time the instruction set as it is
> > obviously not a supported case, but it would be nice to be able to upgrade a
> > "default compilation" at run-time as it is done in rte_acl.
> > I explain this case more clearly for reference:
> >
> > We can have AVX512 supported in the compiler but disable it when compiling
> > (CONFIG_RTE_MACHINE=snb) in order to build a binary running almost
> > everywhere.
> > When running this binary on a CPU having AVX512 support, it will not benefit
> > of the AVX512 improvement.
> > Though, we can compile an AVX512 version of some functions and use them
> > only if the running CPU is capable.
> > This kind of miracle can be achieved in two ways:
> >
> > 1/ For generic C code compiled with a recent GCC, a function can be built for
> > several CPUs thanks to the attribute target_clones.
> >
> > 2/ For manually optimized functions using CPU-specific intrinsics or asm, it is
> > possible to build them with non-default flags thanks to the attribute target.
> >
> > 3/ For manually optimized files using CPU-specific intrinsics or asm, we use
> > specifics flags in the makefile.
> >
> > The function clone in case 1/ is dynamically chosen at run-time through ifunc
> > resolver.
> > The specific functions in cases 2/ and 3/ must chosen at run-time by
> > initializing a function pointer thanks to rte_cpu_get_flag_enabled().
> >
> > Note that rte_hash and software crypto PMDs have a run-time check with
> > rte_cpu_get_flag_enabled() but do not override CFLAGS in the Makefile.
> > Next step for these libraries?
> >
> > Back to rte_memset, I think you should try the solution 2/.
>
> I have read the ACL code, if I understand well , for complex algo implementation,
> it is good idea, but Choosing functions at run time will bring some overhead. For frequently called function
> Which consumes small cycles, the overhead maybe is more than the gains optimizations brings
> For example, for most applications in dpdk, memset only set N = 10 or 12bytes. It consumes fewer cycles.
But then what the point to have an rte_memset() using vector instructions at all?
>From what you are saying the most common case is even less then SSE register size.
Konstantin
>
> Thanks
> Zhiyong
next prev parent reply other threads:[~2016-12-08 9:26 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-05 8:26 [dpdk-dev] [PATCH 0/4] eal/common: introduce rte_memset and related test Zhiyong Yang
2016-12-02 10:00 ` Maxime Coquelin
2016-12-06 6:33 ` Yang, Zhiyong
2016-12-06 8:29 ` Maxime Coquelin
2016-12-07 9:28 ` Yang, Zhiyong
2016-12-07 9:37 ` Yuanhan Liu
2016-12-07 9:43 ` Yang, Zhiyong
2016-12-07 9:48 ` Yuanhan Liu
2016-12-05 8:26 ` [dpdk-dev] [PATCH 1/4] eal/common: introduce rte_memset on IA platform Zhiyong Yang
2016-12-02 10:25 ` Thomas Monjalon
2016-12-08 7:41 ` Yang, Zhiyong
2016-12-08 9:26 ` Ananyev, Konstantin [this message]
2016-12-08 9:53 ` Yang, Zhiyong
2016-12-08 10:27 ` Bruce Richardson
2016-12-08 10:30 ` Ananyev, Konstantin
2016-12-11 12:32 ` Yang, Zhiyong
2016-12-15 6:51 ` Yang, Zhiyong
2016-12-15 10:12 ` Bruce Richardson
2016-12-16 10:19 ` Yang, Zhiyong
2016-12-19 6:27 ` Yuanhan Liu
2016-12-20 2:41 ` Yao, Lei A
2016-12-15 10:53 ` Ananyev, Konstantin
2016-12-16 2:15 ` Yang, Zhiyong
2016-12-16 11:47 ` Ananyev, Konstantin
2016-12-20 9:31 ` Yang, Zhiyong
2016-12-08 15:09 ` Thomas Monjalon
2016-12-11 12:04 ` Yang, Zhiyong
2016-12-27 10:04 ` [dpdk-dev] [PATCH v2 0/4] eal/common: introduce rte_memset and related test Zhiyong Yang
2016-12-27 10:04 ` [dpdk-dev] [PATCH v2 1/4] eal/common: introduce rte_memset on IA platform Zhiyong Yang
2016-12-27 10:04 ` [dpdk-dev] [PATCH v2 2/4] app/test: add functional autotest for rte_memset Zhiyong Yang
2016-12-27 10:04 ` [dpdk-dev] [PATCH v2 3/4] app/test: add performance " Zhiyong Yang
2016-12-27 10:04 ` [dpdk-dev] [PATCH v2 4/4] lib/librte_vhost: improve vhost perf using rte_memset Zhiyong Yang
2017-01-09 9:48 ` [dpdk-dev] [PATCH v2 0/4] eal/common: introduce rte_memset and related test Yang, Zhiyong
2017-01-17 6:24 ` Yang, Zhiyong
2017-01-17 20:14 ` Thomas Monjalon
2017-01-18 0:15 ` Vincent JARDIN
2017-01-18 2:42 ` Yang, Zhiyong
2017-01-18 7:42 ` Thomas Monjalon
2017-01-19 1:36 ` Yang, Zhiyong
2016-12-05 8:26 ` [dpdk-dev] [PATCH 2/4] app/test: add functional autotest for rte_memset Zhiyong Yang
2016-12-05 8:26 ` [dpdk-dev] [PATCH 3/4] app/test: add performance " Zhiyong Yang
2016-12-05 8:26 ` [dpdk-dev] [PATCH 4/4] lib/librte_vhost: improve vhost perf using rte_memset Zhiyong Yang
2016-12-02 9:46 ` Thomas Monjalon
2016-12-06 8:04 ` Yang, Zhiyong
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