[Mesa-dev] [PATCH 2/6] i965/sched: write-after-read dependencies are free

[Jason Ekstrand]

On Fri, Oct 2, 2015 at 2:37 PM, Connor Abbott <cwabbott0 at gmail.com> wrote:
> Although write-after-write dependencies have the same latency as
> read-after-write dependencies due to how the register scoreboard works,
> write-after-read dependencies aren't checked by the EU at all, so
> they're purely a constraint on how the scheduler can order the
> instructions.
>
> Signed-off-by: Connor Abbott <cwabbott0 at gmail.com>
> ---
>  src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp b/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
> index 76d58e2..1652261 100644
> --- a/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
> @@ -927,10 +927,10 @@ fs_instruction_scheduler::calculate_deps()
>           if (inst->src[i].file == GRF) {
>              if (post_reg_alloc) {
>                 for (int r = 0; r < inst->regs_read(i); r++)
> -                  add_dep(n, last_grf_write[inst->src[i].reg + r]);
> +                  add_dep(n, last_grf_write[inst->src[i].reg + r], 0);
>              } else {
>                 for (int r = 0; r < inst->regs_read(i); r++) {
> -                  add_dep(n, last_grf_write[inst->src[i].reg * 16 + inst->src[i].reg_offset + r]);
> +                  add_dep(n, last_grf_write[inst->src[i].reg * 16 + inst->src[i].reg_offset + r], 0);
>                 }
>              }
>           } else if (inst->src[i].file == HW_REG &&
> @@ -941,9 +941,9 @@ fs_instruction_scheduler::calculate_deps()
>                 if (inst->src[i].fixed_hw_reg.vstride == BRW_VERTICAL_STRIDE_0)
>                    size = 1;
>                 for (int r = 0; r < size; r++)
> -                  add_dep(n, last_grf_write[inst->src[i].fixed_hw_reg.nr + r]);
> +                  add_dep(n, last_grf_write[inst->src[i].fixed_hw_reg.nr + r], 0);
>              } else {
> -               add_dep(n, last_fixed_grf_write);
> +               add_dep(n, last_fixed_grf_write, 0);
>              }
>           } else if (inst->src[i].is_accumulator()) {
>              add_dep(n, last_accumulator_write);

You could probably change this one as well, but meh, it's the accumulator...

Reviewed-by: Jason Ekstrand <jason.ekstrand at intel.com>

> --
> 2.1.0
>
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