Un-parallelized OpenACC kernels constructs with nvptx offloading: "avoid offloading"

Thomas Schwinge thomas@codesourcery.com
Wed Feb 10 14:40:00 GMT 2016


On Wed, 10 Feb 2016 14:25:50 +0100, Bernd Schmidt <bschmidt@redhat.com> wrote:
> On 02/10/2016 12:49 PM, Thomas Schwinge wrote:
> > [...]
> I think this has to be considered after gcc-6.

Hmm, I see.

> In general, what's the 
> state of OpenACC these days?

Much improved compared to GCC 5.  :-) Anything specific you'd like me to
elaborate on?  <https://gcc.gnu.org/wiki/OpenACC> should be fairly

> I'm slightly confused by the interface between offloaded code and 
> libgomp. It looks like you're collecting avoid-offloading flags 
> per-function, but then when things get registered, it seems like a 
> per-image flag.

(Per-image flag that affects all offloading for a given offloading type,

> Is that right? It seems like too large a hammer.

Yes, we need a hammer that big: we have to ensure consistency between
data regions on the device and code offloading to the device, as
otherwise we'll very easily run into inconsistencies, because of the
non-shared memory.  In the general case, it's "all or nothing": you
either have to offload all kernels or none of them.

> >> [...]
> Avoid unnecessary braces.
> >> [...]
> Typo.

Thanks for the review; fixed.


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