[dpdk-dev] [PATCH 1/4] eal/common: introduce rte_memset on IA platform

[Yang, Zhiyong]

Hi, Bruce:

> -----Original Message-----
> From: Richardson, Bruce
> Sent: Thursday, December 15, 2016 6:13 PM
> To: Yang, Zhiyong <zhiyong.yang at intel.com>
> Cc: Ananyev, Konstantin <konstantin.ananyev at intel.com>; Thomas
> Monjalon <thomas.monjalon at 6wind.com>; dev at dpdk.org;
> yuanhan.liu at linux.intel.com; De Lara Guarch, Pablo
> <pablo.de.lara.guarch at intel.com>
> Subject: Re: [dpdk-dev] [PATCH 1/4] eal/common: introduce rte_memset on
> IA platform
> 
> On Thu, Dec 15, 2016 at 06:51:08AM +0000, Yang, Zhiyong wrote:
> > Hi, Thomas, Konstantin:
> >
> > > -----Original Message-----
> > > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Yang, Zhiyong
> > > Sent: Sunday, December 11, 2016 8:33 PM
> > > To: Ananyev, Konstantin <konstantin.ananyev at intel.com>; Thomas
> > > Monjalon <thomas.monjalon at 6wind.com>
> > > Cc: dev at dpdk.org; yuanhan.liu at linux.intel.com; Richardson, Bruce
> > > <bruce.richardson at intel.com>; De Lara Guarch, Pablo
> > > <pablo.de.lara.guarch at intel.com>
> > > Subject: Re: [dpdk-dev] [PATCH 1/4] eal/common: introduce
> rte_memset
> > > on IA platform
> > >
> > > Hi, Konstantin, Bruce:
> > >
> > > > -----Original Message-----
> > > > From: Ananyev, Konstantin
> > > > Sent: Thursday, December 8, 2016 6:31 PM
> > > > To: Yang, Zhiyong <zhiyong.yang at intel.com>; Thomas Monjalon
> > > > <thomas.monjalon at 6wind.com>
> > > > Cc: dev at dpdk.org; yuanhan.liu at linux.intel.com; Richardson, Bruce
> > > > <bruce.richardson at intel.com>; De Lara Guarch, Pablo
> > > > <pablo.de.lara.guarch at intel.com>
> > > > Subject: RE: [dpdk-dev] [PATCH 1/4] eal/common: introduce
> > > > rte_memset on IA platform
> > > >
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Yang, Zhiyong
> > > > > Sent: Thursday, December 8, 2016 9:53 AM
> > > > > To: Ananyev, Konstantin <konstantin.ananyev at intel.com>; Thomas
> > > > > Monjalon <thomas.monjalon at 6wind.com>
> > > > > Cc: dev at dpdk.org; yuanhan.liu at linux.intel.com; Richardson, Bruce
> > > > > <bruce.richardson at intel.com>; De Lara Guarch, Pablo
> > > > > <pablo.de.lara.guarch at intel.com>
> > > > > Subject: RE: [dpdk-dev] [PATCH 1/4] eal/common: introduce
> > > > > rte_memset on IA platform
> > > > >
> > > > extern void *(*__rte_memset_vector)( (void *s, int c, size_t n);
> > > >
> > > > static inline void*
> > > > rte_memset_huge(void *s, int c, size_t n) {
> > > >    return __rte_memset_vector(s, c, n); }
> > > >
> > > > static inline void *
> > > > rte_memset(void *s, int c, size_t n) {
> > > > 	If (n < XXX)
> > > > 		return rte_memset_scalar(s, c, n);
> > > > 	else
> > > > 		return rte_memset_huge(s, c, n); }
> > > >
> > > > XXX could be either a define, or could also be a variable, so it
> > > > can be setuped at startup, depending on the architecture.
> > > >
> > > > Would that work?
> > > > Konstantin
> > > >
> > I have implemented the code for  choosing the functions at run time.
> > rte_memcpy is used more frequently, So I test it at run time.
> >
> > typedef void *(*rte_memcpy_vector_t)(void *dst, const void *src,
> > size_t n); extern rte_memcpy_vector_t rte_memcpy_vector; static inline
> > void * rte_memcpy(void *dst, const void *src, size_t n) {
> >         return rte_memcpy_vector(dst, src, n); } In order to reduce
> > the overhead at run time, I assign the function address to var
> > rte_memcpy_vector before main() starts to init the var.
> >
> > static void __attribute__((constructor))
> > rte_memcpy_init(void)
> > {
> > 	if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_AVX2))
> > 	{
> > 		rte_memcpy_vector = rte_memcpy_avx2;
> > 	}
> > 	else if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_SSE4_1))
> > 	{
> > 		rte_memcpy_vector = rte_memcpy_sse;
> > 	}
> > 	else
> > 	{
> > 		rte_memcpy_vector = memcpy;
> > 	}
> >
> > }
> > I run the same virtio/vhost loopback tests without NIC.
> > I can see the  throughput drop  when running choosing functions at run
> > time compared to original code as following on the same platform(my
> machine is haswell)
> > 	Packet size	perf drop
> > 	64 		-4%
> > 	256 		-5.4%
> > 	1024		-5%
> > 	1500		-2.5%
> > Another thing, I run the memcpy_perf_autotest,  when N= <128, the
> > rte_memcpy perf gains almost disappears When choosing functions at run
> > time.  For N=other numbers, the perf gains will become narrow.
> >
> How narrow. How significant is the improvement that we gain from having to
> maintain our own copy of memcpy. If the libc version is nearly as good we
> should just use that.
> 
> /Bruce

Zhihong sent a patch about rte_memcpy,  From the patch,  
we can see the optimization job for memcpy will bring obvious perf improvements
than glibc for DPDK.
http://www.dpdk.org/dev/patchwork/patch/17753/
git log as following:
This patch is tested on Ivy Bridge, Haswell and Skylake, it provides
up to 20% gain for Virtio Vhost PVP traffic, with packet size ranging
from 64 to 1500 bytes.

thanks
Zhiyong