Em ter., 5 de nov. de 2024 às 01:12, Michael Paquier <michael@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.
