[glibc] aarch64: revert memcpy optimze for kunpeng to avoid performance degradation

[glibc] aarch64: revert memcpy optimze for kunpeng to avoid performance degradation

[Szabolcs Nagy]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=28f2ce27722d890a884cc7fa2f6d2bc0cb418f26

commit 28f2ce27722d890a884cc7fa2f6d2bc0cb418f26
Author: Shuo Wang <wangshuo47@huawei.com>
Date:   Wed Jan 20 15:20:44 2021 +0800

    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:
---
 sysdeps/aarch64/multiarch/memcpy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sysdeps/aarch64/multiarch/memcpy.c b/sysdeps/aarch64/multiarch/memcpy.c
index 27259d3386..0e0a5cbcfb 100644
--- 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