Re: define pg_structiszero(addr, s, r)

Hi.

Em seg., 4 de nov. de 2024 às 14:18, Bertrand Drouvot <
bertranddrouvot(dot)pg(at)gmail(dot)com> escreveu:

> Hi,
>
> On Tue, Nov 05, 2024 at 12:24:48AM +1300, David Rowley wrote:
> > On Sat, 2 Nov 2024 at 01:50, Bertrand Drouvot
> > <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> > >
> > > On Fri, Nov 01, 2024 at 09:47:05PM +1300, David Rowley wrote:
> > > > I've attached what I thought a more optimal version might look like
> in
> > > > case anyone thinks making it better is a good idea.
> > > >
> > >
> > > Thanks for the proposal!
> > >
> > > I like the idea, I think that's worth to add a few comments, something
> like:
> >
> > I'm happy if you want to pick this up and continue working on it.
>
> Sure, please find attached v1, the changes are:
>
> - switch from "const char" to "const unsigned char" (could have been done
> in the
> current version of pg_memory_is_all_zeros() though)
> - added some comments
> - adding an Assert for ptr != 0
> - re-introduce the function call in PageIsVerifiedExtended()
> - propose a commit message
>

I think we can add a small optimization to this last patch [1].
The variable *aligned_end* is only needed in the second loop (for).
So, only before the for loop do we actually declare it.

Result before this change:
check zeros using BERTRAND 1 0.000031s

Result after this change:
check zeros using BERTRAND 1 0.000018s

+ const unsigned char *aligned_end;

+ /* Multiple bytes comparison(s) at once */
+ aligned_end = (const unsigned char *) ((uintptr_t) end &
(~(sizeof(size_t) - 1)));
+ for (; p < aligned_end; p += sizeof(size_t))

best regards,
Ranier Vilela

[1] https://godbolt.org/z/fvdzjbnc7