Mesa (master): i965/fs: Add an instruction scheduler.
Eric Anholt
anholt at kemper.freedesktop.org
Thu Jan 20 01:36:53 UTC 2011
Module: Mesa
Branch: master
Commit: 63879d90ace519749fed228ca0e21b5b56c7e1c0
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=63879d90ace519749fed228ca0e21b5b56c7e1c0
Author: Eric Anholt <eric at anholt.net>
Date: Tue Jan 18 17:16:49 2011 -0800
i965/fs: Add an instruction scheduler.
Improves performance of my GLSL demo by 5.1% (+/- 1.4%, n=7). It also
reschedules the giant multiply tree at the end of
glsl-fs-convolution-1 so that we end up not spilling registers,
producing the expected level of performance.
---
src/mesa/drivers/dri/i965/Makefile | 1 +
src/mesa/drivers/dri/i965/brw_fs.cpp | 2 +
src/mesa/drivers/dri/i965/brw_fs.h | 2 +
.../dri/i965/brw_fs_schedule_instructions.cpp | 474 ++++++++++++++++++++
4 files changed, 479 insertions(+), 0 deletions(-)
diff --git a/src/mesa/drivers/dri/i965/Makefile b/src/mesa/drivers/dri/i965/Makefile
index 7c3ac0c..b05ba35 100644
--- a/src/mesa/drivers/dri/i965/Makefile
+++ b/src/mesa/drivers/dri/i965/Makefile
@@ -108,6 +108,7 @@ CXX_SOURCES = \
brw_fs.cpp \
brw_fs_channel_expressions.cpp \
brw_fs_reg_allocate.cpp \
+ brw_fs_schedule_instructions.cpp \
brw_fs_vector_splitting.cpp
ASM_SOURCES =
diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 5b595a3..c24060b 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -3696,6 +3696,8 @@ brw_wm_fs_emit(struct brw_context *brw, struct brw_wm_compile *c)
progress = v.dead_code_eliminate() || progress;
} while (progress);
+ v.schedule_instructions();
+
if (0) {
/* Debug of register spilling: Go spill everything. */
int virtual_grf_count = v.virtual_grf_next;
diff --git a/src/mesa/drivers/dri/i965/brw_fs.h b/src/mesa/drivers/dri/i965/brw_fs.h
index 65c8a1e..7c991f3 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.h
+++ b/src/mesa/drivers/dri/i965/brw_fs.h
@@ -436,6 +436,8 @@ public:
bool dead_code_eliminate();
bool remove_duplicate_mrf_writes();
bool virtual_grf_interferes(int a, int b);
+ void schedule_instructions();
+
void generate_code();
void generate_fb_write(fs_inst *inst);
void generate_linterp(fs_inst *inst, struct brw_reg dst,
diff --git a/src/mesa/drivers/dri/i965/brw_fs_schedule_instructions.cpp b/src/mesa/drivers/dri/i965/brw_fs_schedule_instructions.cpp
new file mode 100644
index 0000000..00aa99d
--- /dev/null
+++ b/src/mesa/drivers/dri/i965/brw_fs_schedule_instructions.cpp
@@ -0,0 +1,474 @@
+/*
+ * Copyright © 2010 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.
+ *
+ * Authors:
+ * Eric Anholt <eric at anholt.net>
+ *
+ */
+
+extern "C" {
+
+#include <sys/types.h>
+
+#include "main/macros.h"
+#include "main/shaderobj.h"
+#include "main/uniforms.h"
+#include "program/prog_optimize.h"
+#include "program/register_allocate.h"
+#include "program/sampler.h"
+#include "program/hash_table.h"
+#include "brw_context.h"
+#include "brw_eu.h"
+#include "brw_wm.h"
+#include "talloc.h"
+}
+#include "brw_fs.h"
+#include "../glsl/glsl_types.h"
+#include "../glsl/ir_optimization.h"
+#include "../glsl/ir_print_visitor.h"
+
+/** @file brw_fs_schedule_instructions.cpp
+ *
+ * List scheduling of FS instructions.
+ *
+ * The basic model of the list scheduler is to take a basic block,
+ * compute a DAG of the dependencies (RAW ordering with latency, WAW
+ * ordering, WAR ordering), and make a list of the DAG heads.
+ * Heuristically pick a DAG head, then put all the children that are
+ * now DAG heads into the list of things to schedule.
+ *
+ * The heuristic is the important part. We're trying to be cheap,
+ * since actually computing the optimal scheduling is NP complete.
+ * What we do is track a "current clock". When we schedule a node, we
+ * update the earliest-unblocked clock time of its children, and
+ * increment the clock. Then, when trying to schedule, we just pick
+ * the earliest-unblocked instruction to schedule.
+ *
+ * Note that often there will be many things which could execute
+ * immediately, and there are a range of heuristic options to choose
+ * from in picking among those.
+ */
+
+class schedule_node : public exec_node
+{
+public:
+ schedule_node(fs_inst *inst)
+ {
+ this->inst = inst;
+ this->child_array_size = 0;
+ this->children = NULL;
+ this->child_latency = NULL;
+ this->child_count = 0;
+ this->parent_count = 0;
+ this->unblocked_time = 0;
+
+ int chans = 8;
+ int math_latency = 22;
+
+ switch (inst->opcode) {
+ case FS_OPCODE_RCP:
+ this->latency = 1 * chans * math_latency;
+ break;
+ case FS_OPCODE_RSQ:
+ this->latency = 2 * chans * math_latency;
+ break;
+ case FS_OPCODE_SQRT:
+ case FS_OPCODE_LOG2:
+ /* full precision log. partial is 2. */
+ this->latency = 3 * chans * math_latency;
+ break;
+ case FS_OPCODE_EXP2:
+ /* full precision. partial is 3, same throughput. */
+ this->latency = 4 * chans * math_latency;
+ break;
+ case FS_OPCODE_POW:
+ this->latency = 8 * chans * math_latency;
+ break;
+ case FS_OPCODE_SIN:
+ case FS_OPCODE_COS:
+ /* minimum latency, max is 12 rounds. */
+ this->latency = 5 * chans * math_latency;
+ break;
+ default:
+ this->latency = 2;
+ break;
+ }
+ }
+
+ fs_inst *inst;
+ schedule_node **children;
+ int *child_latency;
+ int child_count;
+ int parent_count;
+ int child_array_size;
+ int unblocked_time;
+ int latency;
+};
+
+class instruction_scheduler {
+public:
+ instruction_scheduler(fs_visitor *v, void *mem_ctx, int virtual_grf_count)
+ {
+ this->v = v;
+ this->mem_ctx = talloc_new(mem_ctx);
+ this->virtual_grf_count = virtual_grf_count;
+ this->instructions.make_empty();
+ this->instructions_to_schedule = 0;
+ }
+
+ ~instruction_scheduler()
+ {
+ talloc_free(this->mem_ctx);
+ }
+ void add_barrier_deps(schedule_node *n);
+ void add_dep(schedule_node *before, schedule_node *after, int latency);
+
+ void add_inst(fs_inst *inst);
+ void calculate_deps();
+ void schedule_instructions(fs_inst *next_block_header);
+
+ void *mem_ctx;
+
+ int instructions_to_schedule;
+ int virtual_grf_count;
+ exec_list instructions;
+ fs_visitor *v;
+};
+
+void
+instruction_scheduler::add_inst(fs_inst *inst)
+{
+ schedule_node *n = new(mem_ctx) schedule_node(inst);
+
+ assert(!inst->is_head_sentinel());
+ assert(!inst->is_tail_sentinel());
+
+ this->instructions_to_schedule++;
+
+ inst->remove();
+ instructions.push_tail(n);
+}
+
+/**
+ * Add a dependency between two instruction nodes.
+ *
+ * The @after node will be scheduled after @before. We will try to
+ * schedule it @latency cycles after @before, but no guarantees there.
+ */
+void
+instruction_scheduler::add_dep(schedule_node *before, schedule_node *after,
+ int latency)
+{
+ if (!before || !after)
+ return;
+
+ assert(before != after);
+
+ for (int i = 0; i < before->child_count; i++) {
+ if (before->children[i] == after) {
+ before->child_latency[i] = MAX2(before->child_latency[i], latency);
+ return;
+ }
+ }
+
+ if (before->child_array_size <= before->child_count) {
+ if (before->child_array_size < 16)
+ before->child_array_size = 16;
+ else
+ before->child_array_size *= 2;
+
+ before->children = talloc_realloc(mem_ctx, before->children,
+ schedule_node *,
+ before->child_array_size);
+ before->child_latency = talloc_realloc(mem_ctx, before->child_latency,
+ int, before->child_array_size);
+ }
+
+ before->children[before->child_count] = after;
+ before->child_latency[before->child_count] = latency;
+ before->child_count++;
+ after->parent_count++;
+}
+
+/**
+ * Sometimes we really want this node to execute after everything that
+ * was before it and before everything that followed it. This adds
+ * the deps to do so.
+ */
+void
+instruction_scheduler::add_barrier_deps(schedule_node *n)
+{
+ schedule_node *prev = (schedule_node *)n->prev;
+ schedule_node *next = (schedule_node *)n->next;
+
+ if (prev) {
+ while (!prev->is_head_sentinel()) {
+ add_dep(prev, n, 0);
+ prev = (schedule_node *)prev->prev;
+ }
+ }
+
+ if (next) {
+ while (!next->is_tail_sentinel()) {
+ add_dep(n, next, 0);
+ next = (schedule_node *)next->next;
+ }
+ }
+}
+
+void
+instruction_scheduler::calculate_deps()
+{
+ schedule_node *last_grf_write[virtual_grf_count];
+ schedule_node *last_mrf_write[BRW_MAX_MRF];
+ schedule_node *last_conditional_mod = NULL;
+
+ /* The last instruction always needs to still be the last
+ * instruction. Either it's flow control (IF, ELSE, ENDIF, DO,
+ * WHILE) and scheduling other things after it would disturb the
+ * basic block, or it's FB_WRITE and we should do a better job at
+ * dead code elimination anyway.
+ */
+ schedule_node *last = (schedule_node *)instructions.get_tail();
+ add_barrier_deps(last);
+
+ memset(last_grf_write, 0, sizeof(last_grf_write));
+ memset(last_mrf_write, 0, sizeof(last_mrf_write));
+
+ /* top-to-bottom dependencies: RAW and WAW. */
+ foreach_iter(exec_list_iterator, iter, instructions) {
+ schedule_node *n = (schedule_node *)iter.get();
+ fs_inst *inst = n->inst;
+
+ /* read-after-write deps. */
+ for (int i = 0; i < 3; i++) {
+ if (inst->src[i].file == GRF) {
+ if (last_grf_write[inst->src[i].reg]) {
+ add_dep(last_grf_write[inst->src[i].reg], n,
+ last_grf_write[inst->src[i].reg]->latency);
+ }
+ } else if (inst->src[i].file != BAD_FILE &&
+ inst->src[i].file != IMM &&
+ inst->src[i].file != UNIFORM) {
+ assert(inst->src[i].file != MRF);
+ add_barrier_deps(n);
+ }
+ }
+
+ for (int i = 0; i < inst->mlen; i++) {
+ /* It looks like the MRF regs are released in the send
+ * instruction once it's sent, not when the result comes
+ * back.
+ */
+ if (last_mrf_write[inst->base_mrf + i]) {
+ add_dep(last_mrf_write[inst->base_mrf + i], n,
+ last_mrf_write[inst->base_mrf + i]->latency);
+ }
+ }
+
+ if (inst->predicated) {
+ assert(last_conditional_mod);
+ add_dep(last_conditional_mod, n, last_conditional_mod->latency);
+ }
+
+ /* write-after-write deps. */
+ if (inst->dst.file == GRF) {
+ if (last_grf_write[inst->dst.reg]) {
+ add_dep(last_grf_write[inst->dst.reg], n,
+ last_grf_write[inst->dst.reg]->latency);
+ }
+ last_grf_write[inst->dst.reg] = n;
+ } else if (inst->dst.file == MRF) {
+ if (last_mrf_write[inst->dst.hw_reg]) {
+ add_dep(last_mrf_write[inst->dst.hw_reg], n,
+ last_mrf_write[inst->dst.hw_reg]->latency);
+ }
+ last_mrf_write[inst->dst.hw_reg] = n;
+ } else if (inst->dst.file != BAD_FILE) {
+ add_barrier_deps(n);
+ }
+
+ if (inst->mlen > 0) {
+ for (int i = 0; i < v->implied_mrf_writes(inst); i++) {
+ if (last_mrf_write[inst->base_mrf + i]) {
+ add_dep(last_mrf_write[inst->base_mrf + i], n,
+ last_mrf_write[inst->base_mrf + i]->latency);
+ }
+ last_mrf_write[inst->base_mrf + i] = n;
+ }
+ }
+
+ if (inst->conditional_mod) {
+ add_dep(last_conditional_mod, n, 0);
+ last_conditional_mod = n;
+ }
+ }
+
+ /* bottom-to-top dependencies: WAR */
+ memset(last_grf_write, 0, sizeof(last_grf_write));
+ memset(last_mrf_write, 0, sizeof(last_mrf_write));
+ last_conditional_mod = NULL;
+
+ exec_node *node;
+ exec_node *prev;
+ for (node = instructions.get_tail(), prev = node->prev;
+ !node->is_head_sentinel();
+ node = prev, prev = node->prev) {
+ schedule_node *n = (schedule_node *)node;
+ fs_inst *inst = n->inst;
+
+ /* write-after-read deps. */
+ for (int i = 0; i < 3; i++) {
+ if (inst->src[i].file == GRF) {
+ if (last_grf_write[inst->src[i].reg]) {
+ add_dep(n, last_grf_write[inst->src[i].reg], n->latency);
+ }
+ } else if (inst->src[i].file != BAD_FILE &&
+ inst->src[i].file != IMM &&
+ inst->src[i].file != UNIFORM) {
+ assert(inst->src[i].file != MRF);
+ add_barrier_deps(n);
+ }
+ }
+
+ for (int i = 0; i < inst->mlen; i++) {
+ /* It looks like the MRF regs are released in the send
+ * instruction once it's sent, not when the result comes
+ * back.
+ */
+ add_dep(n, last_mrf_write[inst->base_mrf + i], 2);
+ }
+
+ if (inst->predicated) {
+ if (last_conditional_mod) {
+ add_dep(n, last_conditional_mod, n->latency);
+ }
+ }
+
+ /* Update the things this instruction wrote, so earlier reads
+ * can mark this as WAR dependency.
+ */
+ if (inst->dst.file == GRF) {
+ last_grf_write[inst->dst.reg] = n;
+ } else if (inst->dst.file == MRF) {
+ last_mrf_write[inst->dst.hw_reg] = n;
+ } else if (inst->dst.file != BAD_FILE) {
+ add_barrier_deps(n);
+ }
+
+ if (inst->mlen > 0) {
+ for (int i = 0; i < v->implied_mrf_writes(inst); i++) {
+ last_mrf_write[inst->base_mrf + i] = n;
+ }
+ }
+
+ if (inst->conditional_mod)
+ last_conditional_mod = n;
+ }
+}
+
+void
+instruction_scheduler::schedule_instructions(fs_inst *next_block_header)
+{
+ int time = 0;
+
+ /* Remove non-DAG heads from the list. */
+ foreach_iter(exec_list_iterator, iter, instructions) {
+ schedule_node *n = (schedule_node *)iter.get();
+ if (n->parent_count != 0)
+ n->remove();
+ }
+
+ while (!instructions.is_empty()) {
+ schedule_node *chosen = NULL;
+ int chosen_time = 0;
+
+ foreach_iter(exec_list_iterator, iter, instructions) {
+ schedule_node *n = (schedule_node *)iter.get();
+
+ if (!chosen || n->unblocked_time < chosen_time) {
+ chosen = n;
+ chosen_time = n->unblocked_time;
+ }
+ }
+
+ /* Schedule this instruction. */
+ assert(chosen);
+ chosen->remove();
+ next_block_header->insert_before(chosen->inst);
+ instructions_to_schedule--;
+
+ /* Bump the clock. If we expected a delay for scheduling, then
+ * bump the clock to reflect that.
+ */
+ time = MAX2(time + 1, chosen_time);
+
+ /* Now that we've scheduled a new instruction, some of its
+ * children can be promoted to the list of instructions ready to
+ * be scheduled. Update the children's unblocked time for this
+ * DAG edge as we do so.
+ */
+ for (int i = 0; i < chosen->child_count; i++) {
+ schedule_node *child = chosen->children[i];
+
+ child->unblocked_time = MAX2(child->unblocked_time,
+ time + chosen->child_latency[i]);
+
+ child->parent_count--;
+ if (child->parent_count == 0) {
+ instructions.push_tail(child);
+ }
+ }
+ }
+
+ assert(instructions_to_schedule == 0);
+}
+
+void
+fs_visitor::schedule_instructions()
+{
+ fs_inst *next_block_header = (fs_inst *)instructions.head;
+ instruction_scheduler sched(this, mem_ctx, this->virtual_grf_next);
+
+ while (!next_block_header->is_tail_sentinel()) {
+ /* Add things to be scheduled until we get to a new BB. */
+ while (!next_block_header->is_tail_sentinel()) {
+ fs_inst *inst = next_block_header;
+ next_block_header = (fs_inst *)next_block_header->next;
+
+ sched.add_inst(inst);
+ if (inst->opcode == BRW_OPCODE_IF ||
+ inst->opcode == BRW_OPCODE_ELSE ||
+ inst->opcode == BRW_OPCODE_ENDIF ||
+ inst->opcode == BRW_OPCODE_DO ||
+ inst->opcode == BRW_OPCODE_WHILE ||
+ inst->opcode == BRW_OPCODE_BREAK ||
+ inst->opcode == BRW_OPCODE_CONTINUE) {
+ break;
+ }
+ }
+ sched.calculate_deps();
+ sched.schedule_instructions(next_block_header);
+ }
+
+ this->live_intervals_valid = false;
+}
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