Hi,
The integration of the generator is going slowly, but "surely". All the
OpenCL vector kernels (including plane rotations, multi-inner_prod, etc.)
should be device-specific in a few days. This will be a good leap forward,
in terms of maintainability, peak performance and performance-portability.
However, I feel like this is gonna get much more complicated for BLAS3.
Here's why.
Ranges do not work well with zero-padding. The kernel may perform
operations with nonzeros out-of-bound elements, thus giving an incorrect
result ...! Of course, it is mandatory to have each work-group processing
some (blocks) without any difficult size-checking, for performance. I think
that we should drop zero-padding, because it forces us to treat differently
vector and ranges, which we shouldn't have t do, since ranges are vectors,
too. I see two ways of handling GEMM without zero-padding, both of which
have advantages and drawbacks:
(1) Have an optimized kernel for ideal cases (size is a proper multiple of
64/128/Friday/Whatever ; stride{A,B,C} can be incorporated into LDA/LDB ;
start{A,B,C} are multiple of the vector length used in the kernel), and a
fallback kernel for all the other cases. This fallback is super-safe
(size/checking, vector_length=1...)
(2) The same as above, but the optimized kernel is always used for
performing the large sub-matrix multiplication ( rounding the size to the
best previous multiple), and the fallback is just used to finish the job.
I would go for (2), as (1) is simpler to implement but disastrous for large
odd matrices. However, for small matrices (2) will have a large over-head,
and it may be significantly worse than zero-padding in some corner cases
(consider a matrix 60x100000 with either zero-padding to make it 64x100032
or a crappy kernel...). Do you have any idea of how typical BLAS
implementations handle this issue with the offset? (strides are rare enough
to require slow but safe kernel, I believe)
Philippe
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