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

[Bruce Richardson]

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