drm/i915: Use hash tables for the command parser

For clients that submit large batch buffers the command parser has
a substantial impact on performance. On my HSW ULT system performance
drops as much as ~20% on some tests. Most of the time is spent in the
command lookup code. Converting that from the current naive search to
a hash table lookup reduces the performance drop to ~10%.

The choice of value for I915_CMD_HASH_ORDER allows all commands
currently used in the parser tables to hash to their own bucket (except
for one collision on the render ring). The tradeoff is that it wastes
memory. Because the opcodes for the commands in the tables are not
particularly well distributed, reducing the order still leaves many
buckets empty. The increased collisions don't seem to have a huge
impact on the performance gain, but for now anyhow, the parser trades
memory for performance.

NB: Ville noticed that the error paths through the ring init code
will leak memory. I've not addressed that here. We can do a follow
up pass to handle all of the leaks.

v2: improved comment describing selection of hash key mask (Damien)
replace a BUG_ON() with an error return (Tvrtko, Ville)
commit message improvements

Signed-off-by: Brad Volkin <bradley.d.volkin@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_cmd_parser.c

@@ -498,16 +498,18 @@ static u32 gen7_blt_get_cmd_length_mask(u32 cmd_header)
 	return 0;
 }
 
-static bool validate_cmds_sorted(struct intel_ring_buffer *ring)
+static bool validate_cmds_sorted(struct intel_ring_buffer *ring,
+				 const struct drm_i915_cmd_table *cmd_tables,
+				 int cmd_table_count)
 {
 	int i;
 	bool ret = true;
 
-	if (!ring->cmd_tables || ring->cmd_table_count == 0)
+	if (!cmd_tables || cmd_table_count == 0)
 		return true;
 
-	for (i = 0; i < ring->cmd_table_count; i++) {
-		const struct drm_i915_cmd_table *table = &ring->cmd_tables[i];
+	for (i = 0; i < cmd_table_count; i++) {
+		const struct drm_i915_cmd_table *table = &cmd_tables[i];
 		u32 previous = 0;
 		int j;
 
@@ -557,6 +559,68 @@ static bool validate_regs_sorted(struct intel_ring_buffer *ring)
 			     ring->master_reg_count);
 }
 
+struct cmd_node {
+	const struct drm_i915_cmd_descriptor *desc;
+	struct hlist_node node;
+};
+
+/*
+ * Different command ranges have different numbers of bits for the opcode. For
+ * example, MI commands use bits 31:23 while 3D commands use bits 31:16. The
+ * problem is that, for example, MI commands use bits 22:16 for other fields
+ * such as GGTT vs PPGTT bits. If we include those bits in the mask then when
+ * we mask a command from a batch it could hash to the wrong bucket due to
+ * non-opcode bits being set. But if we don't include those bits, some 3D
+ * commands may hash to the same bucket due to not including opcode bits that
+ * make the command unique. For now, we will risk hashing to the same bucket.
+ *
+ * If we attempt to generate a perfect hash, we should be able to look at bits
+ * 31:29 of a command from a batch buffer and use the full mask for that
+ * client. The existing INSTR_CLIENT_MASK/SHIFT defines can be used for this.
+ */
+#define CMD_HASH_MASK STD_MI_OPCODE_MASK
+
+static int init_hash_table(struct intel_ring_buffer *ring,
+			   const struct drm_i915_cmd_table *cmd_tables,
+			   int cmd_table_count)
+{
+	int i, j;
+
+	hash_init(ring->cmd_hash);
+
+	for (i = 0; i < cmd_table_count; i++) {
+		const struct drm_i915_cmd_table *table = &cmd_tables[i];
+
+		for (j = 0; j < table->count; j++) {
+			const struct drm_i915_cmd_descriptor *desc =
+				&table->table[j];
+			struct cmd_node *desc_node =
+				kmalloc(sizeof(*desc_node), GFP_KERNEL);
+
+			if (!desc_node)
+				return -ENOMEM;
+
+			desc_node->desc = desc;
+			hash_add(ring->cmd_hash, &desc_node->node,
+				 desc->cmd.value & CMD_HASH_MASK);
+		}
+	}
+
+	return 0;
+}
+
+static void fini_hash_table(struct intel_ring_buffer *ring)
+{
+	struct hlist_node *tmp;
+	struct cmd_node *desc_node;
+	int i;
+
+	hash_for_each_safe(ring->cmd_hash, i, tmp, desc_node, node) {
+		hash_del(&desc_node->node);
+		kfree(desc_node);
+	}
+}
+
 /**
  * i915_cmd_parser_init_ring() - set cmd parser related fields for a ringbuffer
  * @ring: the ringbuffer to initialize
@@ -564,21 +628,27 @@ static bool validate_regs_sorted(struct intel_ring_buffer *ring)
  * Optionally initializes fields related to batch buffer command parsing in the
  * struct intel_ring_buffer based on whether the platform requires software
  * command parsing.
+ *
+ * Return: non-zero if initialization fails
  */
-void i915_cmd_parser_init_ring(struct intel_ring_buffer *ring)
+int i915_cmd_parser_init_ring(struct intel_ring_buffer *ring)
 {
+	const struct drm_i915_cmd_table *cmd_tables;
+	int cmd_table_count;
+	int ret;
+
 	if (!IS_GEN7(ring->dev))
-		return;
+		return 0;
 
 	switch (ring->id) {
 	case RCS:
 		if (IS_HASWELL(ring->dev)) {
-			ring->cmd_tables = hsw_render_ring_cmds;
-			ring->cmd_table_count =
+			cmd_tables = hsw_render_ring_cmds;
+			cmd_table_count =
 				ARRAY_SIZE(hsw_render_ring_cmds);
 		} else {
-			ring->cmd_tables = gen7_render_cmds;
-			ring->cmd_table_count = ARRAY_SIZE(gen7_render_cmds);
+			cmd_tables = gen7_render_cmds;
+			cmd_table_count = ARRAY_SIZE(gen7_render_cmds);
 		}
 
 		ring->reg_table = gen7_render_regs;
@@ -595,17 +665,17 @@ void i915_cmd_parser_init_ring(struct intel_ring_buffer *ring)
 		ring->get_cmd_length_mask = gen7_render_get_cmd_length_mask;
 		break;
 	case VCS:
-		ring->cmd_tables = gen7_video_cmds;
-		ring->cmd_table_count = ARRAY_SIZE(gen7_video_cmds);
+		cmd_tables = gen7_video_cmds;
+		cmd_table_count = ARRAY_SIZE(gen7_video_cmds);
 		ring->get_cmd_length_mask = gen7_bsd_get_cmd_length_mask;
 		break;
 	case BCS:
 		if (IS_HASWELL(ring->dev)) {
-			ring->cmd_tables = hsw_blt_ring_cmds;
-			ring->cmd_table_count = ARRAY_SIZE(hsw_blt_ring_cmds);
+			cmd_tables = hsw_blt_ring_cmds;
+			cmd_table_count = ARRAY_SIZE(hsw_blt_ring_cmds);
 		} else {
-			ring->cmd_tables = gen7_blt_cmds;
-			ring->cmd_table_count = ARRAY_SIZE(gen7_blt_cmds);
+			cmd_tables = gen7_blt_cmds;
+			cmd_table_count = ARRAY_SIZE(gen7_blt_cmds);
 		}
 
 		ring->reg_table = gen7_blt_regs;
@@ -622,8 +692,8 @@ void i915_cmd_parser_init_ring(struct intel_ring_buffer *ring)
 		ring->get_cmd_length_mask = gen7_blt_get_cmd_length_mask;
 		break;
 	case VECS:
-		ring->cmd_tables = hsw_vebox_cmds;
-		ring->cmd_table_count = ARRAY_SIZE(hsw_vebox_cmds);
+		cmd_tables = hsw_vebox_cmds;
+		cmd_table_count = ARRAY_SIZE(hsw_vebox_cmds);
 		/* VECS can use the same length_mask function as VCS */
 		ring->get_cmd_length_mask = gen7_bsd_get_cmd_length_mask;
 		break;
@@ -633,18 +703,45 @@ void i915_cmd_parser_init_ring(struct intel_ring_buffer *ring)
 		BUG();
 	}
 
-	BUG_ON(!validate_cmds_sorted(ring));
+	BUG_ON(!validate_cmds_sorted(ring, cmd_tables, cmd_table_count));
 	BUG_ON(!validate_regs_sorted(ring));
+
+	ret = init_hash_table(ring, cmd_tables, cmd_table_count);
+	if (ret) {
+		DRM_ERROR("CMD: cmd_parser_init failed!\n");
+		fini_hash_table(ring);
+		return ret;
+	}
+
+	ring->needs_cmd_parser = true;
+
+	return 0;
+}
+
+/**
+ * i915_cmd_parser_fini_ring() - clean up cmd parser related fields
+ * @ring: the ringbuffer to clean up
+ *
+ * Releases any resources related to command parsing that may have been
+ * initialized for the specified ring.
+ */
+void i915_cmd_parser_fini_ring(struct intel_ring_buffer *ring)
+{
+	if (!ring->needs_cmd_parser)
+		return;
+
+	fini_hash_table(ring);
 }
 
 static const struct drm_i915_cmd_descriptor*
-find_cmd_in_table(const struct drm_i915_cmd_table *table,
+find_cmd_in_table(struct intel_ring_buffer *ring,
 		  u32 cmd_header)
 {
-	int i;
+	struct cmd_node *desc_node;
 
-	for (i = 0; i < table->count; i++) {
-		const struct drm_i915_cmd_descriptor *desc = &table->table[i];
+	hash_for_each_possible(ring->cmd_hash, desc_node, node,
+			       cmd_header & CMD_HASH_MASK) {
+		const struct drm_i915_cmd_descriptor *desc = desc_node->desc;
 		u32 masked_cmd = desc->cmd.mask & cmd_header;
 		u32 masked_value = desc->cmd.value & desc->cmd.mask;
 
@@ -668,16 +765,12 @@ find_cmd(struct intel_ring_buffer *ring,
 	 u32 cmd_header,
 	 struct drm_i915_cmd_descriptor *default_desc)
 {
+	const struct drm_i915_cmd_descriptor *desc;
 	u32 mask;
-	int i;
 
-	for (i = 0; i < ring->cmd_table_count; i++) {
-		const struct drm_i915_cmd_descriptor *desc;
-
-		desc = find_cmd_in_table(&ring->cmd_tables[i], cmd_header);
-		if (desc)
-			return desc;
-	}
+	desc = find_cmd_in_table(ring, cmd_header);
+	if (desc)
+		return desc;
 
 	mask = ring->get_cmd_length_mask(cmd_header);
 	if (!mask)
@@ -748,8 +841,7 @@ bool i915_needs_cmd_parser(struct intel_ring_buffer *ring)
 {
 	struct drm_i915_private *dev_priv = ring->dev->dev_private;
 
-	/* No command tables indicates a platform without parsing */
-	if (!ring->cmd_tables)
+	if (!ring->needs_cmd_parser)
 		return false;
 
 	/*

drivers/gpu/drm/i915/i915_drv.h

@@ -2484,7 +2484,8 @@ const char *i915_cache_level_str(int type);
 
 /* i915_cmd_parser.c */
 int i915_cmd_parser_get_version(void);
-void i915_cmd_parser_init_ring(struct intel_ring_buffer *ring);
+int i915_cmd_parser_init_ring(struct intel_ring_buffer *ring);
+void i915_cmd_parser_fini_ring(struct intel_ring_buffer *ring);
 bool i915_needs_cmd_parser(struct intel_ring_buffer *ring);
 int i915_parse_cmds(struct intel_ring_buffer *ring,
 		    struct drm_i915_gem_object *batch_obj,

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1455,7 +1455,9 @@ static int intel_init_ring_buffer(struct drm_device *dev,
 	if (IS_I830(dev) || IS_845G(dev))
 		ring->effective_size -= 2 * CACHELINE_BYTES;
 
-	i915_cmd_parser_init_ring(ring);
+	ret = i915_cmd_parser_init_ring(ring);
+	if (ret)
+		return ret;
 
 	return ring->init(ring);
 }
@@ -1482,6 +1484,8 @@ void intel_cleanup_ring_buffer(struct intel_ring_buffer *ring)
 		ring->cleanup(ring);
 
 	cleanup_status_page(ring);
+
+	i915_cmd_parser_fini_ring(ring);
 }
 
 static int intel_ring_wait_request(struct intel_ring_buffer *ring, int n)

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -1,6 +1,10 @@
 #ifndef _INTEL_RINGBUFFER_H_
 #define _INTEL_RINGBUFFER_H_
 
+#include <linux/hashtable.h>
+
+#define I915_CMD_HASH_ORDER 9
+
 /*
  * Gen2 BSpec "1. Programming Environment" / 1.4.4.6 "Ring Buffer Use"
  * Gen3 BSpec "vol1c Memory Interface Functions" / 2.3.4.5 "Ring Buffer Use"
@@ -176,12 +180,13 @@ struct  intel_ring_buffer {
 		volatile u32 *cpu_page;
 	} scratch;
 
+	bool needs_cmd_parser;
+
 	/*
-	 * Tables of commands the command parser needs to know about
+	 * Table of commands the command parser needs to know about
 	 * for this ring.
 	 */
-	const struct drm_i915_cmd_table *cmd_tables;
-	int cmd_table_count;
+	DECLARE_HASHTABLE(cmd_hash, I915_CMD_HASH_ORDER);
 
 	/*
 	 * Table of registers allowed in commands that read/write registers.