Hi Zhiyong,
> -----Original Message-----
> From: Yang, Zhiyong
> Sent: Thursday, December 15, 2016 6:51 AM
> To: Yang, Zhiyong <[email protected]>; Ananyev, Konstantin
> <[email protected]>; Thomas Monjalon
> <[email protected]>
> Cc: [email protected]; [email protected]; Richardson, Bruce
> <[email protected]>; De Lara Guarch, Pablo
> <[email protected]>
> Subject: RE: [dpdk-dev] [PATCH 1/4] eal/common: introduce rte_memset on IA
> platform
>
> Hi, Thomas, Konstantin:
>
> > -----Original Message-----
> > From: dev [mailto:[email protected]] On Behalf Of Yang, Zhiyong
> > Sent: Sunday, December 11, 2016 8:33 PM
> > To: Ananyev, Konstantin <[email protected]>; Thomas
> > Monjalon <[email protected]>
> > Cc: [email protected]; [email protected]; Richardson, Bruce
> > <[email protected]>; De Lara Guarch, Pablo
> > <[email protected]>
> > 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 <[email protected]>; Thomas Monjalon
> > > <[email protected]>
> > > Cc: [email protected]; [email protected]; Richardson, Bruce
> > > <[email protected]>; De Lara Guarch, Pablo
> > > <[email protected]>
> > > 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 <[email protected]>; Thomas
> > > > Monjalon <[email protected]>
> > > > Cc: [email protected]; [email protected]; Richardson, Bruce
> > > > <[email protected]>; De Lara Guarch, Pablo
> > > > <[email protected]>
> > > > 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 thought we discussed a bit different approach.
In which rte_memcpy_vector() (rte_memeset_vector) would be called only after
some cutoff point, i.e:
void
rte_memcpy(void *dst, const void *src, size_t len)
{
if (len < N) memcpy(dst, src, len);
else rte_memcpy_vector(dst, src, len);
}
If you just always call rte_memcpy_vector() for every len,
then it means that compiler most likely has always to generate a proper call
(not inlining happening).
For small length(s) price of extra function would probably overweight any
potential gain with SSE/AVX2 implementation.
Konstantin
> 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
