Re: [Starpu-devel] Support for half precision

[Samuel Thibault <samuel.thibault@inria.fr>]

Hello,

Getting back to an old pending mail.

Samuel Thibault, le ven. 19 oct. 2018 17:24:57 +0200, a ecrit:
> Hatem Ltaief, le ven. 19 oct. 2018 15:20:24 +0000, a ecrit:
> > We would like to use a tile matrix in single precision to host tiles in 
> > single precision as well as tiles in half precision. When about to 
> > operate on tiles containing half precision data, then only half of the 
> > data tile is meaningful, we would like starpu to transfer only the 
> > meaningful data from the tiles when needed, ie full data tile for single 
> > precision and half data tile for half precision.
> > Basically, you are saying that we can allocate our overall matrix with 
> > tile data structure in single precision, and at the time of the starpu 
> > data registration done on a tile-basis, we should specify the proper 
> > element size.
> > Is that correct?
> 
> Are the half-precision elements contiguous in memory?

>From what I see in the CUBLAS documentation for e.g. cublasHgemm, and SO
like 
https://stackoverflow.com/questions/43120062/cuda-cublas-and-half-precision-data-types
https://stackoverflow.com/questions/32735292/can-anyone-provide-sample-code-demonstrating-the-use-of-16-bit-floating-point-in
they are contiguous. So the overall matrix with tile data structure
needs to be allocated in half precision, and registered to starpu with
the half-precision element size. Probably Chameleon needs to be extended
for that element size.

Now, when you want to mix both single precision and half-precision
parameters for the same task, you'll need to implement the corresponding
CUDA kernel.

Samuel