Mesa (main): pan/bi: Add a bundling heuristic

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Module: Mesa
Branch: main
Commit: ab2cd532ba336d873c8f6b43e5bfb35fe1e7bdc5
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=ab2cd532ba336d873c8f6b43e5bfb35fe1e7bdc5

Author: Alyssa Rosenzweig <alyssa at rosenzweig.io>
Date:   Wed May  5 17:38:02 2021 -0400

pan/bi: Add a bundling heuristic

Pick instructions locally that are likely to minimize nop's globally.
Note the obvious greedy solution is ineffective. Instead the principle
is to choose instructions which will increase _future_ scheduler
freedom, on the assumption that means fewer nop's overall will be
needed.

There is no concern about register pressure and little concern about
message timing, since this is post-RA and message ordering was fixed.

total tuples in shared programs: 125304 -> 123770 (-1.22%)
tuples in affected programs: 88301 -> 86767 (-1.74%)
helped: 548
HURT: 198
helped stats (abs) min: 1.0 max: 31.0 x̄: 3.43 x̃: 2
helped stats (rel) min: 0.33% max: 16.67% x̄: 3.09% x̃: 2.44%
HURT stats (abs)   min: 1.0 max: 12.0 x̄: 1.73 x̃: 1
HURT stats (rel)   min: 0.27% max: 11.11% x̄: 2.82% x̃: 2.35%
95% mean confidence interval for tuples value: -2.39 -1.72
95% mean confidence interval for tuples %-change: -1.77% -1.27%
Tuples are helped.

total clauses in shared programs: 26059 -> 25655 (-1.55%)
clauses in affected programs: 10821 -> 10417 (-3.73%)
helped: 311
HURT: 42
helped stats (abs) min: 1.0 max: 6.0 x̄: 1.44 x̃: 1
helped stats (rel) min: 0.48% max: 16.00% x̄: 5.26% x̃: 5.00%
HURT stats (abs)   min: 1.0 max: 2.0 x̄: 1.05 x̃: 1
HURT stats (rel)   min: 2.13% max: 33.33% x̄: 7.49% x̃: 6.25%
95% mean confidence interval for clauses value: -1.26 -1.02
95% mean confidence interval for clauses %-change: -4.28% -3.21%
Clauses are helped.

total cycles in shared programs: 12154.79 -> 12114.83 (-0.33%)
cycles in affected programs: 1907.63 -> 1867.67 (-2.09%)
helped: 227
HURT: 99
helped stats (abs) min: 0.041665999999999315 max: 1.2083360000000027 x̄: 0.22 x̃: 0
helped stats (rel) min: 0.36% max: 20.00% x̄: 4.14% x̃: 3.85%
HURT stats (abs)   min: 0.041665999999999315 max: 0.5 x̄: 0.09 x̃: 0
HURT stats (rel)   min: 0.28% max: 9.09% x̄: 2.75% x̃: 2.63%
95% mean confidence interval for cycles value: -0.15 -0.09
95% mean confidence interval for cycles %-change: -2.51% -1.59%
Cycles are helped.

total arith in shared programs: 4658.13 -> 4603.42 (-1.17%)
arith in affected programs: 3449.83 -> 3395.12 (-1.59%)
helped: 509
HURT: 249
helped stats (abs) min: 0.041665999999999315 max: 1.2083360000000027 x̄: 0.14 x̃: 0
helped stats (rel) min: 0.36% max: 20.00% x̄: 3.56% x̃: 2.63%
HURT stats (abs)   min: 0.041665999999999315 max: 0.5 x̄: 0.07 x̃: 0
HURT stats (rel)   min: 0.28% max: 25.00% x̄: 3.32% x̃: 2.27%
95% mean confidence interval for arith value: -0.09 -0.06
95% mean confidence interval for arith %-change: -1.64% -0.97%
Arith are helped.

total quadwords in shared programs: 111394 -> 110114 (-1.15%)
quadwords in affected programs: 78074 -> 76794 (-1.64%)
helped: 503
HURT: 204
helped stats (abs) min: 1.0 max: 43.0 x̄: 3.33 x̃: 2
helped stats (rel) min: 0.41% max: 13.79% x̄: 3.02% x̃: 2.44%
HURT stats (abs)   min: 1.0 max: 26.0 x̄: 1.94 x̃: 1
HURT stats (rel)   min: 0.48% max: 7.55% x̄: 2.44% x̃: 2.22%
95% mean confidence interval for quadwords value: -2.16 -1.46
95% mean confidence interval for quadwords %-change: -1.67% -1.21%
Quadwords are helped.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10961>

---

 src/panfrost/bifrost/bi_schedule.c | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/src/panfrost/bifrost/bi_schedule.c b/src/panfrost/bifrost/bi_schedule.c
index 468a9868085..624a002bf29 100644
--- a/src/panfrost/bifrost/bi_schedule.c
+++ b/src/panfrost/bifrost/bi_schedule.c
@@ -1020,10 +1020,27 @@ bi_instr_schedulable(bi_instr *instr,
 }
 
 static signed
-bi_instr_cost(bi_instr *instr)
+bi_instr_cost(bi_instr *instr, struct bi_tuple_state *tuple)
 {
-        /* TODO: stub */
-        return 0;
+        signed cost = 0;
+
+        /* Instructions that can schedule to either FMA or to ADD should be
+         * deprioritized since they're easier to reschedule elsewhere */
+        if (bi_can_fma(instr) && bi_can_add(instr))
+                cost++;
+
+        /* Message-passing instructions impose constraints on the registers
+         * later in the clause, so schedule them as late within a clause as
+         * possible (<==> prioritize them since we're backwards <==> decrease
+         * cost) */
+        if (bi_must_message(instr))
+                cost--;
+
+        /* Last instructions are big constraints (XXX: no effect on shader-db) */
+        if (bi_must_last(instr))
+                cost -= 2;
+
+        return cost;
 }
 
 static unsigned
@@ -1042,9 +1059,14 @@ bi_choose_index(struct bi_worklist st,
                 if (!bi_instr_schedulable(instr, clause, tuple, live_after_temp, fma))
                         continue;
 
-                signed cost = bi_instr_cost(instr);
+                signed cost = bi_instr_cost(instr, tuple);
+
+                /* Tie break in favour of later instructions, under the
+                 * assumption this promotes temporary usage (reducing pressure
+                 * on the register file). This is a side effect of a prepass
+                 * scheduling for pressure. */
 
-                if (cost < best_cost) {
+                if (cost <= best_cost) {
                         best_idx = i;
                         best_cost = cost;
                 }