Removing y avoids cache effects (if y is the size of the L1 cache, the
main array x is removed from it).
Moving init and timing out of the loop makes the scal benchmark behave like
the gemm benchmark, and allows higher accuracy for smaller test cases since
the loop overhead is much smaller than the timing overhead.
Example:
OPENBLAS_LOOPS=10000 ./dscal.goto 1024 8192 1024
on AMD Zen2 (7532) with 32k (4k doubles) L1 cache per core.
Before
From : 1024 To : 8192 Step = 1024 Inc_x = 1 Inc_y = 1 Loops = 10000
SIZE Flops
1024 : 5627.08 MFlops 0.000000 sec
2048 : 5907.34 MFlops 0.000000 sec
3072 : 5553.30 MFlops 0.000001 sec
4096 : 5446.38 MFlops 0.000001 sec
5120 : 5504.61 MFlops 0.000001 sec
6144 : 5501.80 MFlops 0.000001 sec
7168 : 5547.43 MFlops 0.000001 sec
8192 : 5548.46 MFlops 0.000001 sec
After
From : 1024 To : 8192 Step = 1024 Inc_x = 1 Inc_y = 1 Loops = 10000
SIZE Flops
1024 : 6310.28 MFlops 0.000000 sec
2048 : 6396.29 MFlops 0.000000 sec
3072 : 6439.14 MFlops 0.000000 sec
4096 : 6327.14 MFlops 0.000001 sec
5120 : 5628.24 MFlops 0.000001 sec
6144 : 5616.41 MFlops 0.000001 sec
7168 : 5553.13 MFlops 0.000001 sec
8192 : 5600.88 MFlops 0.000001 sec
We can see the L1->L2 switchover point is now where it should be, and the
number of flops for L1 is more accurate.
Bart Oldeman
Qiyu8
Martin Kroeker
Ashwin Sekhar T K
Werner Saar