[gomp-nvptx 2/9] nvptx backend: new "uniform SIMT" codegen variant

Jakub Jelinek jakub@redhat.com
Wed Dec 2 16:36:00 GMT 2015


On Wed, Dec 02, 2015 at 06:44:11PM +0300, Alexander Monakov wrote:
> > But you never know if people actually use #pragma omp simd regions or not,
> > sometimes they will, sometimes they won't, and if the uniform SIMT
> increases
> > power consumption, it might not be desirable.
> 
> It's easy to address: just terminate threads 1-31 if the linked image has
> no SIMD regions, like my pre-simd libgomp was doing.

Well, can't say the linked image in one shared library call a function
in another linked image in another shared library?  Or is that just not
supported for PTX?  I believe XeonPhi supports that.

If each linked image is self-contained, then that is probably a good idea,
but still you could have a single simd region somewhere and lots of other
target regions that don't use simd, or cases where only small amount of time
is spent in a simd region and this wouldn't help in that case.

If the addressables are handled through soft stack, then the rest is mostly
just SSA_NAMEs you can see on the edges of the SIMT region, that really
shouldn't be that expensive to broadcast or reduce back.

	Jakub



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