aarch64: revert memcpy optimze for kunpeng to avoid performance degradation

In commit 863d775c481704baaa41855fc93e5a1ca2dc6bf6, kunpeng920 is added to default memcpy version,
however, there is performance degradation when the copy size is some large bytes, eg: 100k.
This is the result, tested in glibc-2.28:
             before backport  after backport	 Performance improvement
memcpy_1k      0.005              0.005                 0.00%
memcpy_10k     0.032              0.029                 10.34%
memcpy_100k    0.356              0.429                 -17.02%
memcpy_1m      7.470              11.153                -33.02%

This is the demo
#include "stdio.h"
#include "string.h"
#include "stdlib.h"

char a[1024*1024] = {12};
char b[1024*1024] = {13};
int main(int argc, char *argv[])
{
    int i = atoi(argv[1]);
    int j;
    int size = atoi(argv[2]);

    for (j = 0; j < i; j++)
        memcpy(b, a, size*1024);
    return 0;
}

# gcc -g -O0 memcpy.c -o memcpy
# time taskset -c 10 ./memcpy 100000 1024

Co-authored-by: liqingqing <liqingqing3@huawei.com>

diff --git a/sysdeps/aarch64/multiarch/memcpy.c b/sysdeps/aarch64/multiarch/memcpy.c
index 27259d3386c40931e18af18100aebc7763ea6f2b..0e0a5cbcfb1b6dbd7102064bd0245182a4d7cec5 100644 (file)
--- a/sysdeps/aarch64/multiarch/memcpy.c
+++ b/sysdeps/aarch64/multiarch/memcpy.c
@@ -37,7 +37,7 @@ extern __typeof (__redirect_memcpy) __memcpy_falkor attribute_hidden;
 libc_ifunc (__libc_memcpy,
             (IS_THUNDERX (midr)
             ? __memcpy_thunderx
-            : (IS_FALKOR (midr) || IS_PHECDA (midr) || IS_KUNPENG920 (midr)
+            : (IS_FALKOR (midr) || IS_PHECDA (midr)
                ? __memcpy_falkor
                : (IS_THUNDERX2 (midr) || IS_THUNDERX2PA (midr)
                  ? __memcpy_thunderx2