Re: [Qemu-devel] [PATCH v5 08/10] xbzrle: check 8 bytes at a time after an concurrency scene

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* arei.gonglei@huawei.com (arei.gonglei@huawei.com) wrote:
> From: ChenLiang <chenliang88@huawei.com>
> 
> The logic of old code is correct. But Checking byte by byte will
> consume time after an concurrency scene.
> 
> Signed-off-by: ChenLiang <chenliang88@huawei.com>
> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
> ---
>  xbzrle.c | 28 ++++++++++++++++++----------
>  1 file changed, 18 insertions(+), 10 deletions(-)
> 
> diff --git a/xbzrle.c b/xbzrle.c
> index 92cccd7..9d67309 100644
> --- a/xbzrle.c
> +++ b/xbzrle.c
> @@ -51,16 +51,24 @@ int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t *new_buf, int slen,
>  
>          /* word at a time for speed */
>          if (!res) {
> -            while (i < slen &&
> -                   (*(long *)(old_buf + i)) == (*(long *)(new_buf + i))) {
> -                i += sizeof(long);
> -                zrun_len += sizeof(long);
> -            }
> -
> -            /* go over the rest */
> -            while (i < slen && old_buf[i] == new_buf[i]) {
> -                zrun_len++;
> -                i++;
> +            while (i < slen) {
> +                if ((*(long *)(old_buf + i)) == (*(long *)(new_buf + i))) {
> +                    i += sizeof(long);
> +                    zrun_len += sizeof(long);
> +                } else {
> +                    /* go over the rest */
> +                    for (j = 0; j < sizeof(long); j++) {
> +                        if (old_buf[i] == new_buf[i]) {
> +                            i++;
> +                            zrun_len++;
> +                        } else {
> +                            break;
> +                        }
> +                    }
> +                    if (j != sizeof(long)) {
> +                        break;

Is it not possible to make this code the same as the other loop, you could xor in the same
way just change the comparison?
(What do other people think - I was thinking that would just be better since it would
be symmetric?)

Dave
> +                    }
> +                }
>              }
>          }
>  
> -- 
> 1.7.12.4
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK