On (Wed) 10 Dec 2014 [11:55:49], ChenLiang wrote:
> On 2014/12/10 11:18, Amit Shah wrote:
>
> > On (Mon) 24 Nov 2014 [19:55:50], arei.gong...@huawei.com wrote:
> >> From: ChenLiang <chenlian...@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 <chenlian...@huawei.com>
> >> Signed-off-by: Gonglei <arei.gong...@huawei.com>
> >> ---
> >> xbzrle.c | 28 ++++++++++++++++++----------
> >> 1 file changed, 18 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/xbzrle.c b/xbzrle.c
> >> index d27a140..0477367 100644
> >> --- a/xbzrle.c
> >> +++ b/xbzrle.c
> >> @@ -50,16 +50,24 @@ 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++;
> >
> > I don't see how this is different from the code it's replacing. The
> > check and increments are all the same. Difficult to see why there'll
> > be a speed benefit. Can you please explain? Do you have any
> > performance numbers for before/after?
> >
> > Thanks,
> >
> > Amit
> >
> > .
> >
>
> Hi Amit:
>
> + for (j = 0; j < sizeof(long); j++) {
> + if (old_buf[i] == new_buf[i]) {
> + i++;
> + zrun_len++;
> + } else {
> + break;
> + }
> + }
> + if (j != sizeof(long)) {
> + break;
> + }
>
> The branch of *j != sizeof(long)* may not be hit after an concurrency scene.
> so we can continue doing "(*(long *)(old_buf + i)) == (*(long *)(new_buf +
> i))".
> On the another side the old code does "old_buf[i] == new_buf[i]".
Frankly, I still don't see it.
Earlier:
while..
match words
while..
match bytes
Now:
while..
match words
if word mismatch
match bytes
to me, essentially looks the same.
I'll propose to drop this patch till we have a proper justification.
Amit
