[Mesa-dev] [PATCH 2/2] i965: Implement ARB_compute_variable_group_size.

[Ilia Mirkin]

On Mon, Jun 4, 2018 at 4:30 PM, Plamena Manolova
<plamena.n.manolova at gmail.com> wrote:
> Thank you for the review Ilia!
>
> On Fri, 1 Jun 2018 at 23:44, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>
>> On Fri, Jun 1, 2018 at 6:21 PM, Plamena Manolova
>> <plamena.n.manolova at gmail.com> wrote:
>> > +      /*
>> > +       * If the local work group size is variable we have to use a
>> > dispatch
>> > +       * width of 32 here, since at this point we don't know the actual
>> > size of
>> > +       * the workload.
>> > +       */
>> > +      min_dispatch_width = 32;
>>
>> Is that a good idea? You are able to specify a different maximum when
>> using a variable size (MAX_COMPUTE_VARIABLE_GROUP_INVOCATIONS_ARB)
>> s.t. this is 16 (or even 8, although that may be too few for practical
>> use) -- that way you would just set the max to 768 or whatever on
>> gen8+.
>
>
> That's a good point, MAX_COMPUTE_VARIABLE_GROUP_INVOCATIONS_ARB is the
> same on all platforms, so it makes sense to use simd16 instead. Thank you
> for noticing that.

Well IIRC gen7/gen7.5 can do something like 1536 invocations with
SIMD16, while gen8 are down to 768. Either way, not forcing SIMD32 may
be nice -- but that's something for you Intel folk to decide. I just
wanted to point out that you could have different max's for "regular"
compute (where the min max is 1024) and variable-size groups.

  -ilia