On Fri, Sep 18, 2015 at 11:13:03AM +0200, Bernd Schmidt wrote:
> On 09/17/2015 04:40 PM, Nathan Sidwell wrote:
>
> >Added call to gomp_fatal, indicating libgomp is out of date. Also added
> >a default to the switch following with the same effect. The trouble
> >with implementing handling of device_type here now, is difficulty in
> >testing its correctness. If it were buggy we'd be in a worse position
> >than not having it.
>
> Is that so difficult though? See if nvptx ignores (let's say) intelmic
> arguments in favour of the default and accepts nvptx ones.
>
> >+ if (num_waits > 8)
> >+ gomp_fatal ("too many waits for legacy interface");
> >+
> >+ va_start (ap, num_waits);
> >+ for (ix = 0; ix != num_waits; ix++)
> >+ waits[ix] = va_arg (ap, int);
> >+ waits[ix] = 0;
> >+ va_end (ap);
>
> I still don't like this. I think there are at least two better alternatives:
> add a new GOMP_LAUNCH_key which makes GOACC_parallel read a number of waits
> from a va_list * pointer passed after it, or just admit that the legacy
> function always does host fallback and just truncate the current version
> after
>
> if (host_fallback)
> {
> goacc_save_and_set_bind (acc_device_host);
> fn (hostaddrs);
> goacc_restore_bind ();
> return;
> }
>
> (which incidentally ignores all the wait arguments).
Iff GCC 5 compiled offloaded OpenACC/PTX code will always do host fallback
anyway because of the incompatible PTX version, then why don't you just
do
goacc_save_and_set_bind (acc_device_host);
fn (hostaddrs);
goacc_restore_bind ();
and nothing else in GOACC_parallel? If it doesn't always do host fallback,
then I wonder if e.g. the waits wouldn't be better represented as an array
of ints, GOMP_LAUNCH_WAIT op would then encode num_waits and be followed
by a va_arg (ap, int *) with num_waits entries in it. No need to pass
va_list around, instead just the pointer, and the compatibility entry point
would alloca an array, stuff the waits in it and pass GOMP_LAUNCH_WAIT with
the allocated array.
Other than that, I think Bernd has covered all the issues I had.
Jakub
