what is the application scenes of adding optimized Q-register for memcpy

[Szabolcs Nagy]

The 07/25/2020 09:49, wangshuo (AF) wrote:
> this commit 4a733bf375238a6a595033b5785cea7f27d61307 adds optimized
> Q-register memcpy.

please add "aarch64" to the email subject if it's
for aarch64 only.

that commit should not alter the kunpeng920 memcpy.
did you change the ifunc logic to use the new one?

the previous commit increases the entry alignment
and this one may move the memcpy to a slightly
different location in libc.so, but that's about it.

> However, I can not get an ideal results in my enviornment. This is my test:
> 
> test suite: libMicro-0.4.0
> 
> ./memcpy -E -C 200 -L -S -W -N "memcpy_10"    -s 10   -I 10
> ./memcpy -E -C 200 -L -S -W -N "memcpy_1k"    -s 1k   -I 50
> ./memcpy -E -C 200 -L -S -W -N "memcpy_10k"   -s 10k  -I 800
> ./memcpy -E -C 200 -L -S -W -N "memcpy_1m"    -s 1m   -I 500000
> ./memcpy -E -C 200 -L -S -W -N "memcpy_10m"   -s 10m  -I 5000000
> 
> 
> hardware platform:
> Kunpeng-920 @ 2600.0000MHz
> L1d cache: 6 MiB
> L1i cache: 6 MiB
> L2 cache:  48 MiB
> L3 cache:  192 MiB
> 
>            before this commit(usecs)         after this commit(usecs)
> memcpy_10	    0.0065 	                       0.0065
> memcpy_1k	    0.0299 	                       0.0294
> memcpy_10k	    0.2642 	                       0.2642
> memcpy_1m	    27.9040 	                       27.6480
> memcpy_10m	    265.9840 	                       274.6880
> strlen_10	    0.0039 	                       0.0039
> strlen_1k	    0.0571 	                       0.0450
> 
> I was wondering if you could give me some advices about my test results.

3% regression on large copies may be explained by
uarch implementation internals, you can verify
that by keeping the code the same just add some
nop padding around memcpy.