[Mesa-dev] [Mesa-stable] [PATCH] radeonsi/gfx9: reduce max threads per block to 1024 on gfx9+

[Marek Olšák]

Reviewed-by: Marek Olšák <marek.olsak at amd.com>

Marek

On Tue, Jul 25, 2017 at 4:46 PM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
> From: Nicolai Hähnle <nicolai.haehnle at amd.com>
>
> The number of supported waves per thread group has been officially
> reduced to 16 with gfx9 (and trying to use 32 waves causes hangs).
>
> Cc: mesa-stable at lists.freedesktop.org
> ---
>  src/gallium/drivers/radeon/r600_pipe_common.c | 39 ++++++++++++++++-----------
>  1 file changed, 24 insertions(+), 15 deletions(-)
>
> diff --git a/src/gallium/drivers/radeon/r600_pipe_common.c b/src/gallium/drivers/radeon/r600_pipe_common.c
> index fd67d9a..cc52d6b 100644
> --- a/src/gallium/drivers/radeon/r600_pipe_common.c
> +++ b/src/gallium/drivers/radeon/r600_pipe_common.c
> @@ -1024,6 +1024,25 @@ const char *r600_get_llvm_processor_name(enum radeon_family family)
>         }
>  }
>
> +static unsigned get_max_threads_per_block(struct r600_common_screen *screen,
> +                                         enum pipe_shader_ir ir_type)
> +{
> +       if (ir_type != PIPE_SHADER_IR_TGSI)
> +               return 256;
> +
> +       /* Only 16 waves per thread-group on gfx9. */
> +       if (screen->chip_class >= GFX9)
> +               return 1024;
> +
> +       /* Up to 40 waves per thread-group on GCN < gfx9. Expose a nice
> +        * round number.
> +        */
> +       if (screen->chip_class >= SI)
> +               return 2048;
> +
> +       return 256;
> +}
> +
>  static int r600_get_compute_param(struct pipe_screen *screen,
>          enum pipe_shader_ir ir_type,
>          enum pipe_compute_cap param,
> @@ -1078,27 +1097,17 @@ static int r600_get_compute_param(struct pipe_screen *screen,
>         case PIPE_COMPUTE_CAP_MAX_BLOCK_SIZE:
>                 if (ret) {
>                         uint64_t *block_size = ret;
> -                       if (rscreen->chip_class >= SI &&
> -                           ir_type == PIPE_SHADER_IR_TGSI) {
> -                               block_size[0] = 2048;
> -                               block_size[1] = 2048;
> -                               block_size[2] = 2048;
> -                       } else {
> -                               block_size[0] = 256;
> -                               block_size[1] = 256;
> -                               block_size[2] = 256;
> -                       }
> +                       unsigned threads_per_block = get_max_threads_per_block(rscreen, ir_type);
> +                       block_size[0] = threads_per_block;
> +                       block_size[1] = threads_per_block;
> +                       block_size[2] = threads_per_block;
>                 }
>                 return 3 * sizeof(uint64_t);
>
>         case PIPE_COMPUTE_CAP_MAX_THREADS_PER_BLOCK:
>                 if (ret) {
>                         uint64_t *max_threads_per_block = ret;
> -                       if (rscreen->chip_class >= SI &&
> -                           ir_type == PIPE_SHADER_IR_TGSI)
> -                               *max_threads_per_block = 2048;
> -                       else
> -                               *max_threads_per_block = 256;
> +                       *max_threads_per_block = get_max_threads_per_block(rscreen, ir_type);
>                 }
>                 return sizeof(uint64_t);
>         case PIPE_COMPUTE_CAP_ADDRESS_BITS:
> --
> 2.9.3
>
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