Re: [PATCH 03/19] drm/i915: Slightly rework EXEC_OBJECT_CAPTURE handling

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On Mon, Aug 30, 2021 at 02:09:50PM +0200, Maarten Lankhorst wrote:
Use a single null-terminated array for simplicity instead of a linked
list. This might slightly speed up execbuf when many vma's may be marked
as capture, but definitely removes an allocation from a signaling path.

We are not allowed to allocate memory in eb_move_to_gpu, but we can't
enforce it yet through annotations.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>

Looks good to me.
Reviewed-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@xxxxxxxxx>

---
.../gpu/drm/i915/gem/i915_gem_execbuffer.c    | 26 ++++++++++++-------
drivers/gpu/drm/i915/i915_gpu_error.c         |  9 ++++---
drivers/gpu/drm/i915/i915_request.c           |  9 ++-----
drivers/gpu/drm/i915/i915_request.h           |  7 +----
4 files changed, 24 insertions(+), 27 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 8290bdadd167..4f10a81befd1 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -255,6 +255,9 @@ struct i915_execbuffer {
	/** actual size of execobj[] as we may extend it for the cmdparser */
	unsigned int buffer_count;

+	/* Number of objects with EXEC_OBJECT_CAPTURE set */
+	unsigned int capture_count;
+
	/** list of vma not yet bound during reservation phase */
	struct list_head unbound;

@@ -859,6 +862,9 @@ static int eb_lookup_vmas(struct i915_execbuffer *eb)
			goto err;
		}

+		if (eb->exec[i].flags & EXEC_OBJECT_CAPTURE)
+			eb->capture_count++;
+
		err = eb_validate_vma(eb, &eb->exec[i], vma);
		if (unlikely(err)) {
			i915_vma_put(vma);
@@ -1890,16 +1896,8 @@ static int eb_move_to_gpu(struct i915_execbuffer *eb)

		assert_vma_held(vma);

-		if (flags & EXEC_OBJECT_CAPTURE) {
-			struct i915_capture_list *capture;
-
-			capture = kmalloc(sizeof(*capture), GFP_KERNEL);
-			if (capture) {
-				capture->next = eb->request->capture_list;
-				capture->vma = vma;
-				eb->request->capture_list = capture;
-			}
-		}
+		if (flags & EXEC_OBJECT_CAPTURE && eb->request->capture_list)
+			eb->request->capture_list[--eb->capture_count] = vma;

		/*
		 * If the GPU is not _reading_ through the CPU cache, we need
@@ -2828,6 +2826,7 @@ i915_gem_do_execbuffer(struct drm_device *dev,

	eb.fences = NULL;
	eb.num_fences = 0;
+	eb.capture_count = 0;

	eb.batch_flags = 0;
	if (args->flags & I915_EXEC_SECURE) {
@@ -2956,6 +2955,13 @@ i915_gem_do_execbuffer(struct drm_device *dev,
		}
	}

+	if (eb.capture_count) {
+		eb.request->capture_list =
+			kvcalloc(eb.capture_count + 1,
+				 sizeof(*eb.request->capture_list),
+				 GFP_KERNEL | __GFP_NOWARN);
+	}
+
	/*
	 * Whilst this request exists, batch_obj will be on the
	 * active_list, and so will hold the active reference. Only when this
diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index b9f66dbd46bb..44d07923c8d6 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -1355,10 +1355,10 @@ capture_user(struct intel_engine_capture_vma *capture,
	     const struct i915_request *rq,
	     gfp_t gfp)
{
-	struct i915_capture_list *c;
+	int i;

-	for (c = rq->capture_list; c; c = c->next)
-		capture = capture_vma(capture, c->vma, "user", gfp);
+	for (i = 0; rq->capture_list[i]; i++)
+		capture = capture_vma(capture, rq->capture_list[i], "user", gfp);

	return capture;
}
@@ -1406,7 +1406,8 @@ intel_engine_coredump_add_request(struct intel_engine_coredump *ee,
	 * by userspace.
	 */
	vma = capture_vma(vma, rq->batch, "batch", gfp);
-	vma = capture_user(vma, rq, gfp);
+	if (rq->capture_list)
+		vma = capture_user(vma, rq, gfp);
	vma = capture_vma(vma, rq->ring->vma, "ring", gfp);
	vma = capture_vma(vma, rq->context->state, "HW context", gfp);

diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index ce446716d092..4fca2722891c 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -188,15 +188,10 @@ void i915_request_notify_execute_cb_imm(struct i915_request *rq)

static void free_capture_list(struct i915_request *request)
{
-	struct i915_capture_list *capture;
+	struct i915_vma **capture;

	capture = fetch_and_zero(&request->capture_list);
-	while (capture) {
-		struct i915_capture_list *next = capture->next;
-
-		kfree(capture);
-		capture = next;
-	}
+	kvfree(capture);
}

static void __i915_request_fill(struct i915_request *rq, u8 val)
diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
index 1bc1349ba3c2..e7c8cacefcca 100644
--- a/drivers/gpu/drm/i915/i915_request.h
+++ b/drivers/gpu/drm/i915/i915_request.h
@@ -48,11 +48,6 @@ struct drm_i915_gem_object;
struct drm_printer;
struct i915_request;

-struct i915_capture_list {
-	struct i915_capture_list *next;
-	struct i915_vma *vma;
-};
-
#define RQ_TRACE(rq, fmt, ...) do {					\
	const struct i915_request *rq__ = (rq);				\
	ENGINE_TRACE(rq__->engine, "fence %llx:%lld, current %d " fmt,	\
@@ -271,7 +266,7 @@ struct i915_request {
	 * active reference - all objects on this list must also be
	 * on the active_list (of their final request).
	 */
-	struct i915_capture_list *capture_list;
+	struct i915_vma **capture_list;

	/** Time at which this request was emitted, in jiffies. */
	unsigned long emitted_jiffies;
--
2.32.0




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