Em ter., 5 de nov. de 2024 às 01:12, Michael Paquier <mich...@paquier.xyz>
escreveu:
> On Tue, Nov 05, 2024 at 04:23:34PM +1300, David Rowley wrote:
> > I tried your optimisation in the attached allzeros.c and here are my
> results:
> >
> > # My version
> > $ gcc allzeros.c -O2 -o allzeros && for i in {1..3}; do ./allzeros; done
> > char: done in 1543600 nanoseconds
> > size_t: done in 196300 nanoseconds (7.86347 times faster than char)
> >
> > # Ranier's optimization
> > $ gcc allzeros.c -O2 -D RANIERS_OPTIMIZATION -o allzeros && for i in
> > size_t: done in 531700 nanoseconds (3.6545 times faster than char)
> > char: done in 1957200 nanoseconds
>
> I am not seeing numbers as good as yours, but the winner is clear as
> well here:
>
Thanks for testing.
>
> $ gcc allzeros.c -O2 -o allzeros && for i in {1..3}; do
> ./allzeros; done
> char: done in 6578995 nanoseconds
> size_t: done in 829916 nanoseconds (7.9273 times faster than char)
> char: done in 6581465 nanoseconds
> size_t: done in 829948 nanoseconds (7.92997 times faster than char)
> char: done in 6585748 nanoseconds
> size_t: done in 834929 nanoseconds (7.88779 times faster than char)
>
> $ gcc allzeros.c -O2 -D RANIERS_OPTIMIZATION -o allzeros && for i in
> {1..3}; do ./allzeros;
> done char: done in 6591803 nanoseconds
> size_t: done in 1236102 nanoseconds (5.33273 times faster than char)
> char: done in 6606219 nanoseconds
> size_t: done in 1235979 nanoseconds (5.34493 times faster than char)
> char: done in 6594413 nanoseconds
> size_t: done in 1238770 nanoseconds (5.32336 times faster than char)
>
> I'm surprised to see that assigning aligned_end at these two different
> locations has this much effect once the compiler optimizes the
> surroundings, but well.
>
I think that's a plus point for the benefit of not touching the memory if
it's not explicitly necessary.
best regards,
Ranier Vilela
