[dpdk-dev] some questions about rte_memcpy
On 2015/1/22 23:21, Bruce Richardson wrote:
> This (size_c) is a run-time constant, not a compile-time constant. To trigger
> the
> memcpy optimizations inside the compiler, the size value must be constant at
> compile time.
Hi, Bruce
You are right. When use compile-time constant memcpy is faster.Thank you for
all.
Here is my test result:
rte_memcpy(constant) size:8 time:876
rte_memcpy(variable) size:8 time:2824
rte_memcpy(constant) size:16 time:868
rte_memcpy(variable) size:16 time:4436
rte_memcpy(constant) size:32 time:856
rte_memcpy(variable) size:32 time:3264
rte_memcpy(constant) size:48 time:872
rte_memcpy(variable) size:48 time:3972
rte_memcpy(constant) size:64 time:856
rte_memcpy(variable) size:64 time:3644
rte_memcpy(constant) size:128 time:868
rte_memcpy(variable) size:128 time:4720
rte_memcpy(constant) size:256 time:868
rte_memcpy(variable) size:256 time:9624
Here is my test program(Who know how to use a loop to test 'constant memcpy'?):
#include
#include
#include
int main(int narg, char** args)
{
int i,t;
char buf[256];
int tests[7] = {8,16,32,48,64,128,256};
char
buf8[8],buf16[16],buf32[32],buf48[48],buf64[64],buf128[128],buf256[256];
uint64_t start, end;
int times = 999;
uint64_t result_c[7];
if (narg < 2) {
printf("usage:./rte_memcpy_test times\n");
return -1;
}
times = atoi(args[1]);
start = rte_rdtsc();
for(t = 0; t < times; t++) {
rte_memcpy(buf8, buf8, sizeof buf8);
}
end = rte_rdtsc();
result_c[0] = end - start;
start = rte_rdtsc();
for(t = 0; t < times; t++) {
rte_memcpy(buf16, buf16, sizeof buf16);
}
end = rte_rdtsc();
result_c[1] = end - start;
start = rte_rdtsc();
for(t = 0; t < times; t++) {
rte_memcpy(buf32, buf32, sizeof buf32);
}
end = rte_rdtsc();
result_c[2] = end - start;
start = rte_rdtsc();
for(t = 0; t < times; t++) {
rte_memcpy(buf48, buf48, sizeof buf48);
}
end = rte_rdtsc();
result_c[3] = end - start;
start = rte_rdtsc();
for(t = 0; t < times; t++) {
rte_memcpy(buf64, buf64, sizeof buf64);
}
end = rte_rdtsc();
result_c[4] = end - start;
start = rte_rdtsc();
for(t = 0; t < times; t++) {
rte_memcpy(buf128, buf128, sizeof buf128);
}
end = rte_rdtsc();
result_c[5] = end - start;
start = rte_rdtsc();
for(t = 0; t < times; t++) {
rte_memcpy(buf256, buf256, sizeof buf256);
}
end = rte_rdtsc();
result_c[6] = end - start;
for (i = 0; i < (sizeof tests / sizeof tests[0]); i++) {
start = rte_rdtsc();
for(t = 0; t < times; t++) {
rte_memcpy(buf, buf, tests[i]);
}
end = rte_rdtsc();
printf("rte_memcpy(constant) size:%d time:%llu\n", tests[i],
result_c[i]);
printf("rte_memcpy(variable) size:%d time:%llu\n", tests[i],
end - start);
}
return 0;
}
--
Regards,
Haifeng
[dpdk-dev] some questions about rte_memcpy
On 2015/1/22 19:34, Bruce Richardson wrote:
> On Thu, Jan 22, 2015 at 07:23:49PM +0900, Tetsuya Mukawa wrote:
>> On 2015/01/22 16:35, Matthew Hall wrote:
>>> On Thu, Jan 22, 2015 at 01:32:04PM +0800, Linhaifeng wrote:
Do you mean if call rte_memcpy before rte_eal_init() would crash?why?
>>> No guarantee. But a theory. It might use some things from the EAL init to
>>> figure out which version of the accelerated algorithm to use.
>>
>> This selection is done at compile-time.
>> And if the size is constant, I guess DPDK assumes memcpy is replaced by
>> inline __builtin_memcpy.
>> I haven't checked the performance of builtin memcpy, but probably much
>> faster.
>>
>
> Yes, that assumption is correct. A couple of years ago we discovered that for
> constant size values, the compiler would generate much faster code for us
> using a regular memcpy than rte_memcpy, hence the macro.
>
> /Bruce
>
>> Tetsuya
>>
>>> Matthew.
>>
>>
>
>
Hi,Bruce
I test it,most results like you said use constant may be faster,but sometimes
not.
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 16 999
rte_memcpy(constant) used:279893712 @@ not faster
rte_memcpy(variable) used:277818600
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 16 999
rte_memcpy(constant) used:279264328 @@ not faster
rte_memcpy(variable) used:277667116
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 16 999
rte_memcpy(constant) used:279491832 @@ not faster
rte_memcpy(variable) used:277622772
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 32 999
rte_memcpy(constant) used:279402156 @@ not faster
rte_memcpy(variable) used:277738464
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 32 999
rte_memcpy(constant) used:279305172 @@ not faster
rte_memcpy(variable) used:277483004
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 32 999
rte_memcpy(constant) used:279784124 @@ not faster
rte_memcpy(variable) used:277605332
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 48 999
rte_memcpy(constant) used:322817260
rte_memcpy(variable) used:350333864
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 48 999
rte_memcpy(constant) used:322840748
rte_memcpy(variable) used:350297868
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 48 999
rte_memcpy(constant) used:322488240
rte_memcpy(variable) used:350348652
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 64 999
rte_memcpy(constant) used:322021428
rte_memcpy(variable) used:350416440
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 64 999
rte_memcpy(constant) used:321370900
rte_memcpy(variable) used:350355796
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 64 999
rte_memcpy(constant) used:322704552
rte_memcpy(variable) used:349900832
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 128 999
rte_memcpy(constant) used:422705828
rte_memcpy(variable) used:425493328
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 128 999
rte_memcpy(constant) used:422421840 @@ not faster
rte_memcpy(variable) used:413691412
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 128 999
rte_memcpy(constant) used:425233088 @@ not faster
rte_memcpy(variable) used:421136724
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 256 999
rte_memcpy(constant) used:901014608 @@ not faster
rte_memcpy(variable) used:900997388
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 256 999
rte_memcpy(constant) used:900803308 @@ not faster
rte_memcpy(variable) used:900794076
linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 256 999
rte_memcpy(constant) used:901842436 @@ not faster
rte_memcpy(variable) used:901218984
linux-mnSyvH:/mnt/sdb/linhf/test #
here is my test codes:
#include
#include
#include
int main(int narg, char** args)
{
int i;
char buf[1024];
uint64_t start, end;
if (narg < 3) {
printf("usage:./rte_memcpy_test size times\n");
return 0;
}
size_t size_v = atoi(args[1]);
const size_t size_c = atoi(args[1]);
int times = atoi(args[2]);
start = rte_rdtsc();
for(i = 0; i < times; i++) {
rte_memcpy(buf, buf, size_c);
}
end = rte_rdtsc();
printf("rte_memcpy(constant) used:%llu\n", end - start);
start = rte_rdtsc();
for (i = 0; i < times; i++) {
rte_memcpy(buf, buf, size_v);
}
end = rte_rdtsc();
printf("rte_memcpy(variable) used:%llu\n", end - start);
return 0;
}
--
Regards,
Haifeng
[dpdk-dev] some questions about rte_memcpy
On 2015/01/22 16:35, Matthew Hall wrote: > On Thu, Jan 22, 2015 at 01:32:04PM +0800, Linhaifeng wrote: >> Do you mean if call rte_memcpy before rte_eal_init() would crash?why? > No guarantee. But a theory. It might use some things from the EAL init to > figure out which version of the accelerated algorithm to use. This selection is done at compile-time. And if the size is constant, I guess DPDK assumes memcpy is replaced by inline __builtin_memcpy. I haven't checked the performance of builtin memcpy, but probably much faster. Tetsuya > Matthew.
[dpdk-dev] some questions about rte_memcpy
On Thu, Jan 22, 2015 at 08:53:13PM +0800, Linhaifeng wrote:
>
>
> On 2015/1/22 19:34, Bruce Richardson wrote:
> > On Thu, Jan 22, 2015 at 07:23:49PM +0900, Tetsuya Mukawa wrote:
> >> On 2015/01/22 16:35, Matthew Hall wrote:
> >>> On Thu, Jan 22, 2015 at 01:32:04PM +0800, Linhaifeng wrote:
> Do you mean if call rte_memcpy before rte_eal_init() would crash?why?
> >>> No guarantee. But a theory. It might use some things from the EAL init to
> >>> figure out which version of the accelerated algorithm to use.
> >>
> >> This selection is done at compile-time.
> >> And if the size is constant, I guess DPDK assumes memcpy is replaced by
> >> inline __builtin_memcpy.
> >> I haven't checked the performance of builtin memcpy, but probably much
> >> faster.
> >>
> >
> > Yes, that assumption is correct. A couple of years ago we discovered that
> > for
> > constant size values, the compiler would generate much faster code for us
> > using a regular memcpy than rte_memcpy, hence the macro.
> >
> > /Bruce
> >
> >> Tetsuya
> >>
> >>> Matthew.
> >>
> >>
> >
> >
>
> Hi,Bruce
>
> I test it,most results like you said use constant may be faster,but sometimes
> not.
>
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 16 999
> rte_memcpy(constant) used:279893712 @@ not faster
> rte_memcpy(variable) used:277818600
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 16 999
> rte_memcpy(constant) used:279264328 @@ not faster
> rte_memcpy(variable) used:277667116
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 16 999
> rte_memcpy(constant) used:279491832 @@ not faster
> rte_memcpy(variable) used:277622772
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 32 999
> rte_memcpy(constant) used:279402156 @@ not faster
> rte_memcpy(variable) used:277738464
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 32 999
> rte_memcpy(constant) used:279305172 @@ not faster
> rte_memcpy(variable) used:277483004
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 32 999
> rte_memcpy(constant) used:279784124 @@ not faster
> rte_memcpy(variable) used:277605332
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 48 999
> rte_memcpy(constant) used:322817260
> rte_memcpy(variable) used:350333864
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 48 999
> rte_memcpy(constant) used:322840748
> rte_memcpy(variable) used:350297868
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 48 999
> rte_memcpy(constant) used:322488240
> rte_memcpy(variable) used:350348652
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 64 999
> rte_memcpy(constant) used:322021428
> rte_memcpy(variable) used:350416440
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 64 999
> rte_memcpy(constant) used:321370900
> rte_memcpy(variable) used:350355796
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 64 999
> rte_memcpy(constant) used:322704552
> rte_memcpy(variable) used:349900832
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 128 999
> rte_memcpy(constant) used:422705828
> rte_memcpy(variable) used:425493328
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 128 999
> rte_memcpy(constant) used:422421840 @@ not faster
> rte_memcpy(variable) used:413691412
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 128 999
> rte_memcpy(constant) used:425233088 @@ not faster
> rte_memcpy(variable) used:421136724
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 256 999
> rte_memcpy(constant) used:901014608 @@ not faster
> rte_memcpy(variable) used:900997388
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 256 999
> rte_memcpy(constant) used:900803308 @@ not faster
> rte_memcpy(variable) used:900794076
> linux-mnSyvH:/mnt/sdb/linhf/test # ./rte_memcpy_test 256 999
> rte_memcpy(constant) used:901842436 @@ not faster
> rte_memcpy(variable) used:901218984
> linux-mnSyvH:/mnt/sdb/linhf/test #
>
>
>
> here is my test codes:
>
> #include
> #include
> #include
>
>
> int main(int narg, char** args)
> {
> int i;
> char buf[1024];
> uint64_t start, end;
>
> if (narg < 3) {
> printf("usage:./rte_memcpy_test size times\n");
> return 0;
> }
>
> size_t size_v = atoi(args[1]);
> const size_t size_c = atoi(args[1]);
This (size_c) is a run-time constant, not a compile-time constant. To trigger
the
memcpy optimizations inside the compiler, the size value must be constant at
compile time.
Regards,
/Bruce
> int times = atoi(args[2]);
>
> start = rte_rdtsc();
> for(i = 0; i < times; i++) {
> rte_memcpy(buf, buf, size_c);
> }
> end = rte_rdtsc();
> printf("rte_memcpy(constant) used:%llu\n", end - start);
>
> start = rte_rdtsc();
[dpdk-dev] some questions about rte_memcpy
On 2015/1/22 12:45, Matthew Hall wrote: > One theory. Many DPDK functions crash if they are called before > rte_eal_init() > is called. So perhaps this could be a cause, since that won't have been > called > when working on a constant Hi, Matthew Thank you for your response. Do you mean if call rte_memcpy before rte_eal_init() would crash?why? -- Regards, Haifeng
[dpdk-dev] some questions about rte_memcpy
#define rte_memcpy(dst, src, n) \
((__builtin_constant_p(n)) ? \
memcpy((dst), (src), (n)) : \
rte_memcpy_func((dst), (src), (n)))
Why call memcpy when n is constant variable?
Can i change them to the follow codes?
#define rte_memcpy(dst, src, n) \
{ \
int num = n;\
rte_memcpy_func((dst), (src), (num))) \
}
--
Regards,
Haifeng
[dpdk-dev] some questions about rte_memcpy
On Thu, Jan 22, 2015 at 07:23:49PM +0900, Tetsuya Mukawa wrote: > On 2015/01/22 16:35, Matthew Hall wrote: > > On Thu, Jan 22, 2015 at 01:32:04PM +0800, Linhaifeng wrote: > >> Do you mean if call rte_memcpy before rte_eal_init() would crash?why? > > No guarantee. But a theory. It might use some things from the EAL init to > > figure out which version of the accelerated algorithm to use. > > This selection is done at compile-time. > And if the size is constant, I guess DPDK assumes memcpy is replaced by > inline __builtin_memcpy. > I haven't checked the performance of builtin memcpy, but probably much > faster. > Yes, that assumption is correct. A couple of years ago we discovered that for constant size values, the compiler would generate much faster code for us using a regular memcpy than rte_memcpy, hence the macro. /Bruce > Tetsuya > > > Matthew. > >
[dpdk-dev] some questions about rte_memcpy
On Thu, Jan 22, 2015 at 01:32:04PM +0800, Linhaifeng wrote: > Do you mean if call rte_memcpy before rte_eal_init() would crash?why? No guarantee. But a theory. It might use some things from the EAL init to figure out which version of the accelerated algorithm to use. Matthew.
