i965: Reimplement ARB_transform_feedback2 on Haswell and later.

My old implementation accumulated <start, end> pairs in a buffer,
and eventually processed that data on the CPU.  This meant flushing
the batchbuffer and waiting for it to completely execute before we
could map it, resulting in really long stalls.  We could also run out
of space in the buffer, and have to do this early.

Instead, we can use Haswell's MI_MATH command to do the (end - start)
subtraction, as well as the multiplication by 2 or 3 to convert from
the number of primitives written to the number of vertices written.
We still need to CS stall to read the counters, but otherwise everything
is completely pipelined - there's no CPU<->GPU synchronization required.
It also uses only 80 bytes in the buffer, no matter what.

Improves performance in Manhattan on Skylake GT3e at 800x600 by
6.1086% +/- 0.954166% (n=9).  At 1920x1080, improves performance
by 2.82103% +/- 0.148596% (n=84).

v2: Fix number of primitives -> number of vertices calculation for
    GL_TRIANGLES (I was multiplying by 4 instead of 3.)  Caught by
    Jordan Justen.

Signed-off-by: Kenneth Graunke <[email protected]>
Reviewed-by: Jordan Justen <[email protected]>

5 files changed, 318 insertions, 12 deletions

diff --git a/src/mesa/drivers/dri/i965/Makefile.sources b/src/mesa/drivers/dri/i965/Makefile.sources
index 8c60954ee64..d35775ea3ad 100644
--- a/src/mesa/drivers/dri/i965/Makefile.sources
+++ b/src/mesa/drivers/dri/i965/Makefile.sources
@@ -228,6 +228,7 @@ i965_FILES = \
 	gen8_vs_state.c \
 	gen8_wm_depth_stencil.c \
 	hsw_queryobj.c \
+	hsw_sol.c \
 	intel_batchbuffer.c \
 	intel_batchbuffer.h \
 	intel_blit.c \
diff --git a/src/mesa/drivers/dri/i965/brw_context.c b/src/mesa/drivers/dri/i965/brw_context.c
index 1380d4138cf..26514a0c7b6 100644
--- a/src/mesa/drivers/dri/i965/brw_context.c
+++ b/src/mesa/drivers/dri/i965/brw_context.c
@@ -372,13 +372,18 @@ brw_init_driver_functions(struct brw_context *brw,
 
    functions->NewTransformFeedback = brw_new_transform_feedback;
    functions->DeleteTransformFeedback = brw_delete_transform_feedback;
-   functions->GetTransformFeedbackVertexCount =
-      brw_get_transform_feedback_vertex_count;
-   if (brw->gen >= 7) {
+   if (brw->intelScreen->has_mi_math_and_lrr) {
+      functions->BeginTransformFeedback = hsw_begin_transform_feedback;
+      functions->EndTransformFeedback = hsw_end_transform_feedback;
+      functions->PauseTransformFeedback = hsw_pause_transform_feedback;
+      functions->ResumeTransformFeedback = hsw_resume_transform_feedback;
+   } else if (brw->gen >= 7) {
       functions->BeginTransformFeedback = gen7_begin_transform_feedback;
       functions->EndTransformFeedback = gen7_end_transform_feedback;
       functions->PauseTransformFeedback = gen7_pause_transform_feedback;
       functions->ResumeTransformFeedback = gen7_resume_transform_feedback;
+      functions->GetTransformFeedbackVertexCount =
+         brw_get_transform_feedback_vertex_count;
    } else {
       functions->BeginTransformFeedback = brw_begin_transform_feedback;
       functions->EndTransformFeedback = brw_end_transform_feedback;
@@ -494,7 +499,8 @@ brw_initialize_context_constants(struct brw_context *brw)
    ctx->Const.MaxTransformFeedbackSeparateComponents =
       BRW_MAX_SOL_BINDINGS / BRW_MAX_SOL_BUFFERS;
 
-   ctx->Const.AlwaysUseGetTransformFeedbackVertexCount = true;
+   ctx->Const.AlwaysUseGetTransformFeedbackVertexCount =
+      !brw->intelScreen->has_mi_math_and_lrr;
 
    int max_samples;
    const int *msaa_modes = intel_supported_msaa_modes(brw->intelScreen);
diff --git a/src/mesa/drivers/dri/i965/brw_context.h b/src/mesa/drivers/dri/i965/brw_context.h
index b620f14b39f..035cbe9d325 100644
--- a/src/mesa/drivers/dri/i965/brw_context.h
+++ b/src/mesa/drivers/dri/i965/brw_context.h
@@ -1656,6 +1656,20 @@ void
 gen7_resume_transform_feedback(struct gl_context *ctx,
                                struct gl_transform_feedback_object *obj);
 
+/* hsw_sol.c */
+void
+hsw_begin_transform_feedback(struct gl_context *ctx, GLenum mode,
+                             struct gl_transform_feedback_object *obj);
+void
+hsw_end_transform_feedback(struct gl_context *ctx,
+                           struct gl_transform_feedback_object *obj);
+void
+hsw_pause_transform_feedback(struct gl_context *ctx,
+                             struct gl_transform_feedback_object *obj);
+void
+hsw_resume_transform_feedback(struct gl_context *ctx,
+                              struct gl_transform_feedback_object *obj);
+
 /* brw_blorp_blit.cpp */
 GLbitfield
 brw_blorp_framebuffer(struct brw_context *brw,
diff --git a/src/mesa/drivers/dri/i965/brw_draw.c b/src/mesa/drivers/dri/i965/brw_draw.c
index afa8a4e9eae..9d034cfdb33 100644
--- a/src/mesa/drivers/dri/i965/brw_draw.c
+++ b/src/mesa/drivers/dri/i965/brw_draw.c
@@ -153,7 +153,9 @@ trim(GLenum prim, GLuint length)
 static void
 brw_emit_prim(struct brw_context *brw,
               const struct _mesa_prim *prim,
-              uint32_t hw_prim)
+              uint32_t hw_prim,
+              struct brw_transform_feedback_object *xfb_obj,
+              unsigned stream)
 {
    int verts_per_instance;
    int vertex_access_type;
@@ -185,7 +187,7 @@ brw_emit_prim(struct brw_context *brw,
       verts_per_instance = prim->count;
 
    /* If nothing to emit, just return. */
-   if (verts_per_instance == 0 && !prim->is_indirect)
+   if (verts_per_instance == 0 && !prim->is_indirect && !xfb_obj)
       return;
 
    /* If we're set to always flush, do it before and after the primitive emit.
@@ -197,7 +199,25 @@ brw_emit_prim(struct brw_context *brw,
       brw_emit_mi_flush(brw);
 
    /* If indirect, emit a bunch of loads from the indirect BO. */
-   if (prim->is_indirect) {
+   if (xfb_obj) {
+      indirect_flag = GEN7_3DPRIM_INDIRECT_PARAMETER_ENABLE;
+
+      brw_load_register_mem(brw, GEN7_3DPRIM_VERTEX_COUNT,
+                            xfb_obj->prim_count_bo,
+                            I915_GEM_DOMAIN_VERTEX, 0,
+                            stream * sizeof(uint32_t));
+      BEGIN_BATCH(9);
+      OUT_BATCH(MI_LOAD_REGISTER_IMM | (9 - 2));
+      OUT_BATCH(GEN7_3DPRIM_INSTANCE_COUNT);
+      OUT_BATCH(prim->num_instances);
+      OUT_BATCH(GEN7_3DPRIM_START_VERTEX);
+      OUT_BATCH(0);
+      OUT_BATCH(GEN7_3DPRIM_BASE_VERTEX);
+      OUT_BATCH(0);
+      OUT_BATCH(GEN7_3DPRIM_START_INSTANCE);
+      OUT_BATCH(0);
+      ADVANCE_BATCH();
+   } else if (prim->is_indirect) {
       struct gl_buffer_object *indirect_buffer = brw->ctx.DrawIndirectBuffer;
       drm_intel_bo *bo = intel_bufferobj_buffer(brw,
             intel_buffer_object(indirect_buffer),
@@ -382,6 +402,8 @@ brw_try_draw_prims(struct gl_context *ctx,
                    const struct _mesa_index_buffer *ib,
                    GLuint min_index,
                    GLuint max_index,
+                   struct brw_transform_feedback_object *xfb_obj,
+                   unsigned stream,
                    struct gl_buffer_object *indirect)
 {
    struct brw_context *brw = brw_context(ctx);
@@ -531,7 +553,7 @@ retry:
 	 brw_upload_render_state(brw);
       }
 
-      brw_emit_prim(brw, &prims[i], brw->primitive);
+      brw_emit_prim(brw, &prims[i], brw->primitive, xfb_obj, stream);
 
       brw->no_batch_wrap = false;
 
@@ -573,14 +595,14 @@ brw_draw_prims(struct gl_context *ctx,
                GLboolean index_bounds_valid,
                GLuint min_index,
                GLuint max_index,
-               struct gl_transform_feedback_object *unused_tfb_object,
+               struct gl_transform_feedback_object *gl_xfb_obj,
                unsigned stream,
                struct gl_buffer_object *indirect)
 {
    struct brw_context *brw = brw_context(ctx);
    const struct gl_client_array **arrays = ctx->Array._DrawArrays;
-
-   assert(unused_tfb_object == NULL);
+   struct brw_transform_feedback_object *xfb_obj =
+      (struct brw_transform_feedback_object *) gl_xfb_obj;
 
    if (!brw_check_conditional_render(brw))
       return;
@@ -619,7 +641,7 @@ brw_draw_prims(struct gl_context *ctx,
     * to it.
     */
    brw_try_draw_prims(ctx, arrays, prims, nr_prims, ib, min_index, max_index,
-                      indirect);
+                      xfb_obj, stream, indirect);
 }
 
 void
diff --git a/src/mesa/drivers/dri/i965/hsw_sol.c b/src/mesa/drivers/dri/i965/hsw_sol.c
new file mode 100644
index 00000000000..ef8fcf48346
--- /dev/null
+++ b/src/mesa/drivers/dri/i965/hsw_sol.c
@@ -0,0 +1,263 @@
+/*
+ * Copyright © 2016 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+/**
+ * An implementation of the transform feedback driver hooks for Haswell
+ * and later hardware.  This uses MI_MATH to compute the number of vertices
+ * written (for use by DrawTransformFeedback()) without any CPU<->GPU
+ * synchronization which could stall.
+ */
+
+#include "brw_context.h"
+#include "brw_state.h"
+#include "brw_defines.h"
+#include "intel_batchbuffer.h"
+#include "intel_buffer_objects.h"
+#include "main/transformfeedback.h"
+
+/**
+ * We store several values in obj->prim_count_bo:
+ *
+ * [4x 32-bit values]: Final Number of Vertices Written
+ * [4x 32-bit values]: Tally of Primitives Written So Far
+ * [4x 64-bit values]: Starting SO_NUM_PRIMS_WRITTEN Counter Snapshots
+ *
+ * The first set of values is used by DrawTransformFeedback(), which
+ * copies one of them into the 3DPRIM_VERTEX_COUNT register and performs
+ * an indirect draw.  The other values are just temporary storage.
+ */
+
+#define TALLY_OFFSET (BRW_MAX_XFB_STREAMS * sizeof(uint32_t))
+#define START_OFFSET (TALLY_OFFSET * 2)
+
+/**
+ * Store the SO_NUM_PRIMS_WRITTEN counters for each stream (4 uint64_t values)
+ * to prim_count_bo.
+ */
+static void
+save_prim_start_values(struct brw_context *brw,
+                       struct brw_transform_feedback_object *obj)
+{
+   /* Flush any drawing so that the counters have the right values. */
+   brw_emit_mi_flush(brw);
+
+   /* Emit MI_STORE_REGISTER_MEM commands to write the values. */
+   for (int i = 0; i < BRW_MAX_XFB_STREAMS; i++) {
+      brw_store_register_mem64(brw, obj->prim_count_bo,
+                               GEN7_SO_NUM_PRIMS_WRITTEN(i),
+                               START_OFFSET + i * sizeof(uint64_t));
+   }
+}
+
+/**
+ * Compute the number of primitives written during our most recent
+ * transform feedback activity (the current SO_NUM_PRIMS_WRITTEN value
+ * minus the stashed "start" value), and add it to our running tally.
+ *
+ * If \p finalize is true, also compute the number of vertices written
+ * (by multiplying by the number of vertices per primitive), and store
+ * that to the "final" location.
+ *
+ * Otherwise, just overwrite the old tally with the new one.
+ */
+static void
+tally_prims_written(struct brw_context *brw,
+                    struct brw_transform_feedback_object *obj,
+                    bool finalize)
+{
+   /* Flush any drawing so that the counters have the right values. */
+   brw_emit_mi_flush(brw);
+
+   for (int i = 0; i < BRW_MAX_XFB_STREAMS; i++) {
+      /* GPR0 = Tally */
+      brw_load_register_imm32(brw, HSW_CS_GPR(0) + 4, 0);
+      brw_load_register_mem(brw, HSW_CS_GPR(0), obj->prim_count_bo,
+                            I915_GEM_DOMAIN_INSTRUCTION,
+                            I915_GEM_DOMAIN_INSTRUCTION,
+                            TALLY_OFFSET + i * sizeof(uint32_t));
+      /* GPR1 = Start Snapshot */
+      brw_load_register_mem64(brw, HSW_CS_GPR(1), obj->prim_count_bo,
+                              I915_GEM_DOMAIN_INSTRUCTION,
+                              I915_GEM_DOMAIN_INSTRUCTION,
+                              START_OFFSET + i * sizeof(uint64_t));
+      /* GPR2 = Ending Snapshot */
+      brw_load_register_reg64(brw, GEN7_SO_NUM_PRIMS_WRITTEN(i), HSW_CS_GPR(2));
+
+      BEGIN_BATCH(9);
+      OUT_BATCH(HSW_MI_MATH | (9 - 2));
+      /* GPR1 = GPR2 (End) - GPR1 (Start) */
+      OUT_BATCH(MI_MATH_ALU2(LOAD, SRCA, R2));
+      OUT_BATCH(MI_MATH_ALU2(LOAD, SRCB, R1));
+      OUT_BATCH(MI_MATH_ALU0(SUB));
+      OUT_BATCH(MI_MATH_ALU2(STORE, R1, ACCU));
+      /* GPR0 = GPR0 (Tally) + GPR1 (Diff) */
+      OUT_BATCH(MI_MATH_ALU2(LOAD, SRCA, R0));
+      OUT_BATCH(MI_MATH_ALU2(LOAD, SRCB, R1));
+      OUT_BATCH(MI_MATH_ALU0(ADD));
+      OUT_BATCH(MI_MATH_ALU2(STORE, R0, ACCU));
+      ADVANCE_BATCH();
+
+      if (!finalize) {
+         /* Write back the new tally */
+         brw_store_register_mem32(brw, obj->prim_count_bo, HSW_CS_GPR(0),
+                                  TALLY_OFFSET + i * sizeof(uint32_t));
+      } else {
+         /* Convert the number of primitives to the number of vertices. */
+         if (obj->primitive_mode == GL_LINES) {
+            /* Double R0 (R0 = R0 + R0) */
+            BEGIN_BATCH(5);
+            OUT_BATCH(HSW_MI_MATH | (5 - 2));
+            OUT_BATCH(MI_MATH_ALU2(LOAD, SRCA, R0));
+            OUT_BATCH(MI_MATH_ALU2(LOAD, SRCB, R0));
+            OUT_BATCH(MI_MATH_ALU0(ADD));
+            OUT_BATCH(MI_MATH_ALU2(STORE, R0, ACCU));
+            ADVANCE_BATCH();
+         } else if (obj->primitive_mode == GL_TRIANGLES) {
+            /* Triple R0 (R1 = R0 + R0, R0 = R0 + R1) */
+            BEGIN_BATCH(9);
+            OUT_BATCH(HSW_MI_MATH | (9 - 2));
+            OUT_BATCH(MI_MATH_ALU2(LOAD, SRCA, R0));
+            OUT_BATCH(MI_MATH_ALU2(LOAD, SRCB, R0));
+            OUT_BATCH(MI_MATH_ALU0(ADD));
+            OUT_BATCH(MI_MATH_ALU2(STORE, R1, ACCU));
+            OUT_BATCH(MI_MATH_ALU2(LOAD, SRCA, R0));
+            OUT_BATCH(MI_MATH_ALU2(LOAD, SRCB, R1));
+            OUT_BATCH(MI_MATH_ALU0(ADD));
+            OUT_BATCH(MI_MATH_ALU2(STORE, R0, ACCU));
+            ADVANCE_BATCH();
+         }
+         /* Store it to the final result */
+         brw_store_register_mem32(brw, obj->prim_count_bo, HSW_CS_GPR(0),
+                                  i * sizeof(uint32_t));
+      }
+   }
+}
+
+/**
+ * BeginTransformFeedback() driver hook.
+ */
+void
+hsw_begin_transform_feedback(struct gl_context *ctx, GLenum mode,
+                              struct gl_transform_feedback_object *obj)
+{
+   struct brw_context *brw = brw_context(ctx);
+   struct brw_transform_feedback_object *brw_obj =
+      (struct brw_transform_feedback_object *) obj;
+
+   brw_obj->primitive_mode = mode;
+
+   /* Reset the SO buffer offsets to 0. */
+   if (brw->gen >= 8) {
+      brw_obj->zero_offsets = true;
+   } else {
+      BEGIN_BATCH(1 + 2 * BRW_MAX_XFB_STREAMS);
+      OUT_BATCH(MI_LOAD_REGISTER_IMM | (1 + 2 * BRW_MAX_XFB_STREAMS - 2));
+      for (int i = 0; i < BRW_MAX_XFB_STREAMS; i++) {
+         OUT_BATCH(GEN7_SO_WRITE_OFFSET(i));
+         OUT_BATCH(0);
+      }
+      ADVANCE_BATCH();
+   }
+
+   /* Zero out the initial tallies */
+   brw_store_data_imm64(brw, brw_obj->prim_count_bo, TALLY_OFFSET,     0ull);
+   brw_store_data_imm64(brw, brw_obj->prim_count_bo, TALLY_OFFSET + 8, 0ull);
+
+   /* Store the new starting value of the SO_NUM_PRIMS_WRITTEN counters. */
+   save_prim_start_values(brw, brw_obj);
+}
+
+/**
+ * PauseTransformFeedback() driver hook.
+ */
+void
+hsw_pause_transform_feedback(struct gl_context *ctx,
+                              struct gl_transform_feedback_object *obj)
+{
+   struct brw_context *brw = brw_context(ctx);
+   struct brw_transform_feedback_object *brw_obj =
+      (struct brw_transform_feedback_object *) obj;
+
+   if (brw->is_haswell) {
+      /* Save the SOL buffer offset register values. */
+      for (int i = 0; i < BRW_MAX_XFB_STREAMS; i++) {
+         BEGIN_BATCH(3);
+         OUT_BATCH(MI_STORE_REGISTER_MEM | (3 - 2));
+         OUT_BATCH(GEN7_SO_WRITE_OFFSET(i));
+         OUT_RELOC(brw_obj->offset_bo,
+                   I915_GEM_DOMAIN_INSTRUCTION, I915_GEM_DOMAIN_INSTRUCTION,
+                   i * sizeof(uint32_t));
+         ADVANCE_BATCH();
+      }
+   }
+
+   /* Add any primitives written to our tally */
+   tally_prims_written(brw, brw_obj, false);
+}
+
+/**
+ * ResumeTransformFeedback() driver hook.
+ */
+void
+hsw_resume_transform_feedback(struct gl_context *ctx,
+                               struct gl_transform_feedback_object *obj)
+{
+   struct brw_context *brw = brw_context(ctx);
+   struct brw_transform_feedback_object *brw_obj =
+      (struct brw_transform_feedback_object *) obj;
+
+   if (brw->is_haswell) {
+      /* Reload the SOL buffer offset registers. */
+      for (int i = 0; i < BRW_MAX_XFB_STREAMS; i++) {
+         BEGIN_BATCH(3);
+         OUT_BATCH(GEN7_MI_LOAD_REGISTER_MEM | (3 - 2));
+         OUT_BATCH(GEN7_SO_WRITE_OFFSET(i));
+         OUT_RELOC(brw_obj->offset_bo,
+                   I915_GEM_DOMAIN_INSTRUCTION, I915_GEM_DOMAIN_INSTRUCTION,
+                   i * sizeof(uint32_t));
+         ADVANCE_BATCH();
+      }
+   }
+
+   /* Store the new starting value of the SO_NUM_PRIMS_WRITTEN counters. */
+   save_prim_start_values(brw, brw_obj);
+}
+
+/**
+ * EndTransformFeedback() driver hook.
+ */
+void
+hsw_end_transform_feedback(struct gl_context *ctx,
+			    struct gl_transform_feedback_object *obj)
+{
+   struct brw_context *brw = brw_context(ctx);
+   struct brw_transform_feedback_object *brw_obj =
+      (struct brw_transform_feedback_object *) obj;
+
+   /* Add any primitives written to our tally, convert it from the number
+    * of primitives written to the number of vertices written, and store
+    * it in the "final" location in the buffer which DrawTransformFeedback()
+    * will use as the vertex count.
+    */
+   tally_prims_written(brw, brw_obj, true);
+}