[v8, 1/5] powerpc/64: Align bytes before fall back to .Lshort in powerpc64 memcmp()

[Michael Ellerman]

On Thu, 2018-06-07 at 01:57:51 UTC, wei.guo.simon at gmail.com wrote:
> From: Simon Guo <wei.guo.simon at gmail.com>
> 
> Currently memcmp() 64bytes version in powerpc will fall back to .Lshort
> (compare per byte mode) if either src or dst address is not 8 bytes aligned.
> It can be opmitized in 2 situations:
> 
> 1) if both addresses are with the same offset with 8 bytes boundary:
> memcmp() can compare the unaligned bytes within 8 bytes boundary firstly
> and then compare the rest 8-bytes-aligned content with .Llong mode.
> 
> 2)  If src/dst addrs are not with the same offset of 8 bytes boundary:
> memcmp() can align src addr with 8 bytes, increment dst addr accordingly,
>  then load src with aligned mode and load dst with unaligned mode.
> 
> This patch optmizes memcmp() behavior in the above 2 situations.
> 
> Tested with both little/big endian. Performance result below is based on
> little endian.
> 
> Following is the test result with src/dst having the same offset case:
> (a similar result was observed when src/dst having different offset):
> (1) 256 bytes
> Test with the existing tools/testing/selftests/powerpc/stringloops/memcmp:
> - without patch
> 	29.773018302 seconds time elapsed                                          ( +- 0.09% )
> - with patch
> 	16.485568173 seconds time elapsed                                          ( +-  0.02% )
> 		-> There is ~+80% percent improvement
> 
> (2) 32 bytes
> To observe performance impact on < 32 bytes, modify
> tools/testing/selftests/powerpc/stringloops/memcmp.c with following:
> -------
>  #include <string.h>
>  #include "utils.h"
> 
> -#define SIZE 256
> +#define SIZE 32
>  #define ITERATIONS 10000
> 
>  int test_memcmp(const void *s1, const void *s2, size_t n);
> --------
> 
> - Without patch
> 	0.244746482 seconds time elapsed                                          ( +-  0.36%)
> - with patch
> 	0.215069477 seconds time elapsed                                          ( +-  0.51%)
> 		-> There is ～+13% improvement
> 
> (3) 0~8 bytes
> To observe <8 bytes performance impact, modify
> tools/testing/selftests/powerpc/stringloops/memcmp.c with following:
> -------
>  #include <string.h>
>  #include "utils.h"
> 
> -#define SIZE 256
> -#define ITERATIONS 10000
> +#define SIZE 8
> +#define ITERATIONS 1000000
> 
>  int test_memcmp(const void *s1, const void *s2, size_t n);
> -------
> - Without patch
>        1.845642503 seconds time elapsed                                          ( +- 0.12% )
> - With patch
>        1.849767135 seconds time elapsed                                          ( +- 0.26% )
> 		-> They are nearly the same. (-0.2%)
> 
> Signed-off-by: Simon Guo <wei.guo.simon at gmail.com>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/2d9ee327adce5f6becea2dd51d282a

cheers