drm/i915: Async GPU relocation processing

If the user requires patching of their batch or auxiliary buffers, we
currently make the alterations on the cpu. If they are active on the GPU
at the time, we wait under the struct_mutex for them to finish executing
before we rewrite the contents. This happens if shared relocation trees
are used between different contexts with separate address space (and the
buffers then have different addresses in each), the 3D state will need
to be adjusted between execution on each context. However, we don't need
to use the CPU to do the relocation patching, as we could queue commands
to the GPU to perform it and use fences to serialise the operation with
the current activity and future - so the operation on the GPU appears
just as atomic as performing it immediately. Performing the relocation
rewrites on the GPU is not free, in terms of pure throughput, the number
of relocations/s is about halved - but more importantly so is the time
under the struct_mutex.

v2: Break out the request/batch allocation for clearer error flow.
v3: A few asserts to ensure rq ordering is maintained
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/i915_gem.c

@@ -4397,7 +4397,6 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915,
 		GEM_BUG_ON(i915_gem_object_is_active(obj));
 		list_for_each_entry_safe(vma, vn,
 					 &obj->vma_list, obj_link) {
-			GEM_BUG_ON(!i915_vma_is_ggtt(vma));
 			GEM_BUG_ON(i915_vma_is_active(vma));
 			vma->flags &= ~I915_VMA_PIN_MASK;
 			i915_vma_close(vma);

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -40,7 +40,12 @@
 #include "intel_drv.h"
 #include "intel_frontbuffer.h"
 
-#define DBG_USE_CPU_RELOC 0 /* -1 force GTT relocs; 1 force CPU relocs */
+enum {
+	FORCE_CPU_RELOC = 1,
+	FORCE_GTT_RELOC,
+	FORCE_GPU_RELOC,
+#define DBG_FORCE_RELOC 0 /* choose one of the above! */
+};
 
 #define __EXEC_OBJECT_HAS_REF		BIT(31)
 #define __EXEC_OBJECT_HAS_PIN		BIT(30)
@@ -212,10 +217,15 @@ struct i915_execbuffer {
 		struct drm_mm_node node; /** temporary GTT binding */
 		unsigned long vaddr; /** Current kmap address */
 		unsigned long page; /** Currently mapped page index */
+		unsigned int gen; /** Cached value of INTEL_GEN */
 		bool use_64bit_reloc : 1;
 		bool has_llc : 1;
 		bool has_fence : 1;
 		bool needs_unfenced : 1;
+
+		struct drm_i915_gem_request *rq;
+		u32 *rq_cmd;
+		unsigned int rq_size;
 	} reloc_cache;
 
 	u64 invalid_flags; /** Set of execobj.flags that are invalid */
@@ -496,8 +506,11 @@ static inline int use_cpu_reloc(const struct reloc_cache *cache,
 	if (!i915_gem_object_has_struct_page(obj))
 		return false;
 
-	if (DBG_USE_CPU_RELOC)
-		return DBG_USE_CPU_RELOC > 0;
+	if (DBG_FORCE_RELOC == FORCE_CPU_RELOC)
+		return true;
+
+	if (DBG_FORCE_RELOC == FORCE_GTT_RELOC)
+		return false;
 
 	return (cache->has_llc ||
 		obj->cache_dirty ||
@@ -887,6 +900,8 @@ static void eb_reset_vmas(const struct i915_execbuffer *eb)
 
 static void eb_destroy(const struct i915_execbuffer *eb)
 {
+	GEM_BUG_ON(eb->reloc_cache.rq);
+
 	if (eb->lut_size >= 0)
 		kfree(eb->buckets);
 }
@@ -904,11 +919,14 @@ static void reloc_cache_init(struct reloc_cache *cache,
 	cache->page = -1;
 	cache->vaddr = 0;
 	/* Must be a variable in the struct to allow GCC to unroll. */
+	cache->gen = INTEL_GEN(i915);
 	cache->has_llc = HAS_LLC(i915);
-	cache->has_fence = INTEL_GEN(i915) < 4;
-	cache->needs_unfenced = INTEL_INFO(i915)->unfenced_needs_alignment;
 	cache->use_64bit_reloc = HAS_64BIT_RELOC(i915);
+	cache->has_fence = cache->gen < 4;
+	cache->needs_unfenced = INTEL_INFO(i915)->unfenced_needs_alignment;
 	cache->node.allocated = false;
+	cache->rq = NULL;
+	cache->rq_size = 0;
 }
 
 static inline void *unmask_page(unsigned long p)
@@ -930,10 +948,24 @@ static inline struct i915_ggtt *cache_to_ggtt(struct reloc_cache *cache)
 	return &i915->ggtt;
 }
 
+static void reloc_gpu_flush(struct reloc_cache *cache)
+{
+	GEM_BUG_ON(cache->rq_size >= cache->rq->batch->obj->base.size / sizeof(u32));
+	cache->rq_cmd[cache->rq_size] = MI_BATCH_BUFFER_END;
+	i915_gem_object_unpin_map(cache->rq->batch->obj);
+	i915_gem_chipset_flush(cache->rq->i915);
+
+	__i915_add_request(cache->rq, true);
+	cache->rq = NULL;
+}
+
 static void reloc_cache_reset(struct reloc_cache *cache)
 {
 	void *vaddr;
 
+	if (cache->rq)
+		reloc_gpu_flush(cache);
+
 	if (!cache->vaddr)
 		return;
 
@@ -1099,6 +1131,121 @@ static void clflush_write32(u32 *addr, u32 value, unsigned int flushes)
 		*addr = value;
 }
 
+static int __reloc_gpu_alloc(struct i915_execbuffer *eb,
+			     struct i915_vma *vma,
+			     unsigned int len)
+{
+	struct reloc_cache *cache = &eb->reloc_cache;
+	struct drm_i915_gem_object *obj;
+	struct drm_i915_gem_request *rq;
+	struct i915_vma *batch;
+	u32 *cmd;
+	int err;
+
+	GEM_BUG_ON(vma->obj->base.write_domain & I915_GEM_DOMAIN_CPU);
+
+	obj = i915_gem_batch_pool_get(&eb->engine->batch_pool, PAGE_SIZE);
+	if (IS_ERR(obj))
+		return PTR_ERR(obj);
+
+	cmd = i915_gem_object_pin_map(obj,
+				      cache->has_llc ? I915_MAP_WB : I915_MAP_WC);
+	i915_gem_object_unpin_pages(obj);
+	if (IS_ERR(cmd))
+		return PTR_ERR(cmd);
+
+	err = i915_gem_object_set_to_wc_domain(obj, false);
+	if (err)
+		goto err_unmap;
+
+	batch = i915_vma_instance(obj, vma->vm, NULL);
+	if (IS_ERR(batch)) {
+		err = PTR_ERR(batch);
+		goto err_unmap;
+	}
+
+	err = i915_vma_pin(batch, 0, 0, PIN_USER | PIN_NONBLOCK);
+	if (err)
+		goto err_unmap;
+
+	rq = i915_gem_request_alloc(eb->engine, eb->ctx);
+	if (IS_ERR(rq)) {
+		err = PTR_ERR(rq);
+		goto err_unpin;
+	}
+
+	err = i915_gem_request_await_object(rq, vma->obj, true);
+	if (err)
+		goto err_request;
+
+	err = eb->engine->emit_flush(rq, EMIT_INVALIDATE);
+	if (err)
+		goto err_request;
+
+	err = i915_switch_context(rq);
+	if (err)
+		goto err_request;
+
+	err = eb->engine->emit_bb_start(rq,
+					batch->node.start, PAGE_SIZE,
+					cache->gen > 5 ? 0 : I915_DISPATCH_SECURE);
+	if (err)
+		goto err_request;
+
+	GEM_BUG_ON(!reservation_object_test_signaled_rcu(obj->resv, true));
+	i915_vma_move_to_active(batch, rq, 0);
+	reservation_object_lock(obj->resv, NULL);
+	reservation_object_add_excl_fence(obj->resv, &rq->fence);
+	reservation_object_unlock(obj->resv);
+	i915_vma_unpin(batch);
+
+	i915_vma_move_to_active(vma, rq, true);
+	reservation_object_lock(vma->obj->resv, NULL);
+	reservation_object_add_excl_fence(vma->obj->resv, &rq->fence);
+	reservation_object_unlock(vma->obj->resv);
+
+	rq->batch = batch;
+
+	cache->rq = rq;
+	cache->rq_cmd = cmd;
+	cache->rq_size = 0;
+
+	/* Return with batch mapping (cmd) still pinned */
+	return 0;
+
+err_request:
+	i915_add_request(rq);
+err_unpin:
+	i915_vma_unpin(batch);
+err_unmap:
+	i915_gem_object_unpin_map(obj);
+	return err;
+}
+
+static u32 *reloc_gpu(struct i915_execbuffer *eb,
+		      struct i915_vma *vma,
+		      unsigned int len)
+{
+	struct reloc_cache *cache = &eb->reloc_cache;
+	u32 *cmd;
+
+	if (cache->rq_size > PAGE_SIZE/sizeof(u32) - (len + 1))
+		reloc_gpu_flush(cache);
+
+	if (unlikely(!cache->rq)) {
+		int err;
+
+		err = __reloc_gpu_alloc(eb, vma, len);
+		if (unlikely(err))
+			return ERR_PTR(err);
+	}
+
+	cmd = cache->rq_cmd + cache->rq_size;
+	cache->rq_size += len;
+
+	return cmd;
+}
+
 static u64
 relocate_entry(struct i915_vma *vma,
 	       const struct drm_i915_gem_relocation_entry *reloc,
@@ -1111,6 +1258,67 @@ relocate_entry(struct i915_vma *vma,
 	bool wide = eb->reloc_cache.use_64bit_reloc;
 	void *vaddr;
 
+	if (!eb->reloc_cache.vaddr &&
+	    (DBG_FORCE_RELOC == FORCE_GPU_RELOC ||
+	     !reservation_object_test_signaled_rcu(obj->resv, true))) {
+		const unsigned int gen = eb->reloc_cache.gen;
+		unsigned int len;
+		u32 *batch;
+		u64 addr;
+
+		if (wide)
+			len = offset & 7 ? 8 : 5;
+		else if (gen >= 4)
+			len = 4;
+		else if (gen >= 3)
+			len = 3;
+		else /* On gen2 MI_STORE_DWORD_IMM uses a physical address */
+			goto repeat;
+
+		batch = reloc_gpu(eb, vma, len);
+		if (IS_ERR(batch))
+			goto repeat;
+
+		addr = gen8_canonical_addr(vma->node.start + offset);
+		if (wide) {
+			if (offset & 7) {
+				*batch++ = MI_STORE_DWORD_IMM_GEN4;
+				*batch++ = lower_32_bits(addr);
+				*batch++ = upper_32_bits(addr);
+				*batch++ = lower_32_bits(target_offset);
+
+				addr = gen8_canonical_addr(addr + 4);
+
+				*batch++ = MI_STORE_DWORD_IMM_GEN4;
+				*batch++ = lower_32_bits(addr);
+				*batch++ = upper_32_bits(addr);
+				*batch++ = upper_32_bits(target_offset);
+			} else {
+				*batch++ = (MI_STORE_DWORD_IMM_GEN4 | (1 << 21)) + 1;
+				*batch++ = lower_32_bits(addr);
+				*batch++ = upper_32_bits(addr);
+				*batch++ = lower_32_bits(target_offset);
+				*batch++ = upper_32_bits(target_offset);
+			}
+		} else if (gen >= 6) {
+			*batch++ = MI_STORE_DWORD_IMM_GEN4;
+			*batch++ = 0;
+			*batch++ = addr;
+			*batch++ = target_offset;
+		} else if (gen >= 4) {
+			*batch++ = MI_STORE_DWORD_IMM_GEN4 | MI_USE_GGTT;
+			*batch++ = 0;
+			*batch++ = addr;
+			*batch++ = target_offset;
+		} else {
+			*batch++ = MI_STORE_DWORD_IMM | MI_MEM_VIRTUAL;
+			*batch++ = addr;
+			*batch++ = target_offset;
+		}
+
+		goto out;
+	}
+
 repeat:
 	vaddr = reloc_vaddr(obj, &eb->reloc_cache, offset >> PAGE_SHIFT);
 	if (IS_ERR(vaddr))
@@ -1127,6 +1335,7 @@ relocate_entry(struct i915_vma *vma,
 		goto repeat;
 	}
 
+out:
 	return target->node.start | UPDATE;
 }
 
@@ -1189,7 +1398,8 @@ eb_relocate_entry(struct i915_execbuffer *eb,
 	 * If the relocation already has the right value in it, no
 	 * more work needs to be done.
 	 */
-	if (gen8_canonical_addr(target->node.start) == reloc->presumed_offset)
+	if (!DBG_FORCE_RELOC &&
+	    gen8_canonical_addr(target->node.start) == reloc->presumed_offset)
 		return 0;
 
 	/* Check that the relocation address is valid... */
@@ -1915,7 +2125,7 @@ i915_gem_do_execbuffer(struct drm_device *dev,
 	eb.i915 = to_i915(dev);
 	eb.file = file;
 	eb.args = args;
-	if (!(args->flags & I915_EXEC_NO_RELOC))
+	if (DBG_FORCE_RELOC || !(args->flags & I915_EXEC_NO_RELOC))
 		args->flags |= __EXEC_HAS_RELOC;
 	eb.exec = exec;
 	eb.ctx = NULL;
@@ -2068,6 +2278,9 @@ i915_gem_do_execbuffer(struct drm_device *dev,
 		eb.batch = vma;
 	}
 
+	/* All GPU relocation batches must be submitted prior to the user rq */
+	GEM_BUG_ON(eb.reloc_cache.rq);
+
 	/* Allocate a request for this batch buffer nice and early. */
 	eb.request = i915_gem_request_alloc(eb.engine, eb.ctx);
 	if (IS_ERR(eb.request)) {