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

[Yang, Zhiyong]

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.

Thanks
Zhiyong