Re: [PATCH 1/5] OpenACC 2.0 support for libgomp - OpenACC runtime, NVidia PTX/CUDA plugin (repost)

[Thomas Schwinge <thomas@codesourcery.com>]

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Hi!

On Wed, 12 Nov 2014 11:06:26 +0100, Jakub Jelinek <jakub@redhat.com> wrote:
> On Tue, Nov 11, 2014 at 01:53:23PM +0000, Julian Brown wrote:
> > +# TODO.  See testsuite/lib/libgomp.exp:libgomp_init.
> > +INTERNAL {
> > +  global:
> > +	initialize_env;
> > +};

This should not have been part of the upstream trunk submission -- it is
an internal change, which also is not present on gomp-4_0-branch.

> Ugh, I don't like that.

Neither do I.  ;-/

> If it is a hack around dejagnu deficiency, then
> perhaps dejagnu should be changed or gcc *.exp adjusted, if it is for
> all programs, then there should be some way how to communicate passing
> state from the host to the target plugin.

There is no mechanism in DejaGnu to pass environment variables to remote
boards (which we're using in internal testing), and we currently use that
to circle through available accelerators/libgomp plugins: by setting the
ACC_DEVICE_TYPE environment variable.  For that, we have to pre-set that
environment variable before libgomp initializes, which is difficult (or,
not possible), because libgomp's initialization is done via a constructor
attribute, and it is not possible from the "main" executable to preempt a
dependent shared library's constructors, so we have to "re-initialize"
later on...

This clearly is a hack, was never meant for upstream, and should be
replaced by a different scheme: my idea was that GCC should expose to
libgomp the first offloading device, T1, that has been specified with
-foffload=T1,T2,..., (defaulting to a GCC configure-time list), and then
T1 would be used as the default device for OpenACC.  This T1,T2,... list
could also serve to map the numeric device clause ID enumeration in
OpenMP?  (As far as I'm aware, there is no scheme in OpenMP to map from
"descriptive" device names (intelmic, nvptx, ...) to the numeric IDs used
with the device clause?)


Grüße,
 Thomas

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