[Mesa-dev] [PATCH 1/1] r600: Enable FMA on chips that support it

[Glenn Kennard]

On Wed, 15 Jun 2016 20:13:13 +0200, Jan Vesely <jan.vesely at rutgers.edu> wrote:

> Signed-off-by: Jan Vesely <jan.vesely at rutgers.edu>
> ---
> Untested (I don't have the required hw)
>
>  src/gallium/drivers/r600/r600_pipe.c   | 5 ++++-
>  src/gallium/drivers/r600/r600_shader.c | 2 +-
>  2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/src/gallium/drivers/r600/r600_pipe.c b/src/gallium/drivers/r600/r600_pipe.c
> index a49b00f..49c3e1d 100644
> --- a/src/gallium/drivers/r600/r600_pipe.c
> +++ b/src/gallium/drivers/r600/r600_pipe.c
> @@ -548,7 +548,6 @@ static int r600_get_shader_param(struct pipe_screen* pscreen, unsigned shader, e
>  		return 0;
>  	case PIPE_SHADER_CAP_TGSI_DROUND_SUPPORTED:
>  	case PIPE_SHADER_CAP_TGSI_DFRACEXP_DLDEXP_SUPPORTED:
> -	case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
>  	case PIPE_SHADER_CAP_MAX_SHADER_BUFFERS:
>  	case PIPE_SHADER_CAP_MAX_SHADER_IMAGES:
>  		return 0;
> @@ -558,6 +557,10 @@ static int r600_get_shader_param(struct pipe_screen* pscreen, unsigned shader, e
>  		 *    https://bugs.freedesktop.org/show_bug.cgi?id=86720
>  		 */
>  		return 255;
> +	case PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED:
> +		// Enable on CYPRESS(EG) and CAYMAN(NI)
> +		return rscreen->b.family == CHIP_CYPRESS ||
> +		       rscreen->b.family == CHIP_CAYMAN;
>  	}
>  	return 0;
>  }
> diff --git a/src/gallium/drivers/r600/r600_shader.c b/src/gallium/drivers/r600/r600_shader.c
> index 101f666..35019e3 100644
> --- a/src/gallium/drivers/r600/r600_shader.c
> +++ b/src/gallium/drivers/r600/r600_shader.c
> @@ -8917,7 +8917,7 @@ static const struct r600_shader_tgsi_instruction r600_shader_tgsi_instruction[]
>  	[TGSI_OPCODE_MAD]	= { ALU_OP3_MULADD, tgsi_op3},
>  	[TGSI_OPCODE_SUB]	= { ALU_OP2_ADD, tgsi_op2},
>  	[TGSI_OPCODE_LRP]	= { ALU_OP0_NOP, tgsi_lrp},
> -	[TGSI_OPCODE_FMA]	= { ALU_OP0_NOP, tgsi_unsupported},
> +	[TGSI_OPCODE_FMA]	= { ALU_OP3_FMA, tgsi_op3},
>  	[TGSI_OPCODE_SQRT]	= { ALU_OP1_SQRT_IEEE, tgsi_trans_srcx_replicate},
>  	[TGSI_OPCODE_DP2A]	= { ALU_OP0_NOP, tgsi_unsupported},
>  	[22]			= { ALU_OP0_NOP, tgsi_unsupported},

You probably meant to add the opcode to the eg_shader_tgsi_instruction and cm_shader_tgsi_instruction opcode tables rather than the R600/R700 one?


I'll also note in passing that FMA on CYPRESS/HEMLOCK has an issue rate of 4/cycle vs MULADD 5/cycle since FMA cannot be issued in the 't' slot,
may or may not affect performance depending on if the GLSL front end decides to use fma for mul+add operations. On Cayman/Aruba they are the same rate.


/Glenn