On Thursday, August 14, 2014 01:11:39 PM Iago Toral Quiroga wrote:
> This implements the FF_SYNC message required in gen6 geometry shaders to
> get the initial URB handle.
> ---
> src/mesa/drivers/dri/i965/brw_defines.h | 14 +++++++++
> src/mesa/drivers/dri/i965/brw_shader.cpp | 2 ++
> src/mesa/drivers/dri/i965/brw_vec4.h | 3 ++
> src/mesa/drivers/dri/i965/brw_vec4_generator.cpp | 40
> ++++++++++++++++++++++++
> 4 files changed, 59 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_defines.h
> b/src/mesa/drivers/dri/i965/brw_defines.h
> index 3564041..125d728 100644
> --- a/src/mesa/drivers/dri/i965/brw_defines.h
> +++ b/src/mesa/drivers/dri/i965/brw_defines.h
> @@ -1002,6 +1002,20 @@ enum opcode {
> * - dst is the GRF for gl_InvocationID.
> */
> GS_OPCODE_GET_INSTANCE_ID,
> +
> + /**
> + * Send a FF_SYNC message to allocate initial URB handles (gen6).
> + *
> + * - dst will hold the newly allocated VUE handle. It is expected to be
> + * be initialized so that it can be used to as the FF_SYNC message
> header
> + * (that is, it won't do an implied move from R0).
> + *
> + * - src0 is a temporary that will be used as writeback register for the
> + * FF_SYNC operation.
I was originally a bit concerned that writing over a source register could get
your into trouble - say, optimization passes not noticing that you're modifying
src0, or the scheduler not noticing dependencies. But, since you allocate a
temporary, and only use it in this one instruction, there's not really any
chance for optimizations to combine it with anything.
So, I suppose this will work.
Another way you might consider doing this...
1. Add GS_OPCODE_FF_SYNC to vec4_visitor::implied_mrf_writes, and return 1.
This tells the scheduler etc. that you implicitly trash 1 MRF.
2. Make the visitor set inst->base_mrf, and MOV <base_mrf> g0.
3. Make the generator use brw_message_reg(inst->base_mrf) for the header MOVs.
Then, src0 can be the number of primitives written, and you don't need src1.
That seems simpler to me.
brw_ff_sync will resolve your GRF (dst) to an MRF anyway; the above approach
would write directly into the MRF, saving you a GRF.
Thoughts?
> + *
> + * - src1 is the number of primitives written.
> + */
> + GS_OPCODE_FF_SYNC,
> };
>
> enum brw_urb_write_flags {
> diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp
> b/src/mesa/drivers/dri/i965/brw_shader.cpp
> index 0033135..5749061 100644
> --- a/src/mesa/drivers/dri/i965/brw_shader.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
> @@ -528,6 +528,8 @@ brw_instruction_name(enum opcode op)
> return "set_channel_masks";
> case GS_OPCODE_GET_INSTANCE_ID:
> return "get_instance_id";
> + case GS_OPCODE_FF_SYNC:
> + return "ff_sync";
>
> default:
> /* Yes, this leaks. It's in debug code, it should never occur, and if
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4.h
> b/src/mesa/drivers/dri/i965/brw_vec4.h
> index 67132c0..72fabdd 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4.h
> +++ b/src/mesa/drivers/dri/i965/brw_vec4.h
> @@ -659,6 +659,9 @@ private:
> void generate_gs_prepare_channel_masks(struct brw_reg dst);
> void generate_gs_set_channel_masks(struct brw_reg dst, struct brw_reg
> src);
> void generate_gs_get_instance_id(struct brw_reg dst);
> + void generate_gs_ff_sync(struct brw_reg dst,
> + struct brw_reg src0,
> + struct brw_reg src1);
> void generate_oword_dual_block_offsets(struct brw_reg m1,
> struct brw_reg index);
> void generate_scratch_write(vec4_instruction *inst,
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
> b/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
> index c63b47a..05f4892 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
> @@ -621,6 +621,42 @@ vec4_generator::generate_gs_get_instance_id(struct
> brw_reg dst)
> }
>
> void
> +vec4_generator::generate_gs_ff_sync(struct brw_reg dst,
> + struct brw_reg src0,
> + struct brw_reg src1)
> +{
> + /* We use dst to setup the ff_sync header, so we expect it to be
> + * initialized to R0 by the caller. Here we overwrite dword 0 (cleared
> + * for now since we are not doing transform feedback) and dword 1
> + * (to hold the number of primitives written).
> + */
> + brw_push_insn_state(p);
> + brw_set_default_mask_control(p, BRW_MASK_DISABLE);
> + brw_set_default_access_mode(p, BRW_ALIGN_1);
> + brw_MOV(p, get_element_ud(dst, 0), brw_imm_ud(0));
> + brw_MOV(p, get_element_ud(dst, 1), get_element_ud(src1, 0));
> + brw_set_default_access_mode(p, BRW_ALIGN_16);
> + brw_pop_insn_state(p);
> +
> + /* Write allocated URB handle to temporary passed in src0 */
> + brw_ff_sync(p,
> + src0,
> + 0,
> + dst,
> + 1, /* allocate */
> + 1, /* response length */
> + 0 /* eot */);
> +
> + /* Now put allocated urb handle in dst.0 */
> + brw_push_insn_state(p);
> + brw_set_default_access_mode(p, BRW_ALIGN_1);
> + brw_set_default_mask_control(p, BRW_MASK_DISABLE);
> + brw_MOV(p, get_element_ud(dst, 0), get_element_ud(src0, 0));
> + brw_set_default_access_mode(p, BRW_ALIGN_16);
> + brw_pop_insn_state(p);
> +}
> +
> +void
> vec4_generator::generate_oword_dual_block_offsets(struct brw_reg m1,
> struct brw_reg index)
> {
> @@ -1198,6 +1234,10 @@
> vec4_generator::generate_vec4_instruction(vec4_instruction *instruction,
> generate_gs_get_instance_id(dst);
> break;
>
> + case GS_OPCODE_FF_SYNC:
> + generate_gs_ff_sync(dst, src[0], src[1]);
> + break;
> +
> case SHADER_OPCODE_SHADER_TIME_ADD:
> brw_shader_time_add(p, src[0],
> prog_data->base.binding_table.shader_time_start);
>
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