[PATCH 06/28] drm/i915: Squash repeated awaits on the same fence

Chris Wilson chris at chris-wilson.co.uk
Tue Apr 18 11:27:59 UTC 2017


Track the latest fence waited upon on each context, and only add a new
asynchronous wait if the new fence is more recent than the recorded
fence for that context. This requires us to filter out unordered
timelines, which are noted by DMA_FENCE_NO_CONTEXT. However, in the
absence of a universal identifier, we have to use our own
i915->mm.unordered_timeline token.

v2: Throw around the debug crutches
v3: Inline the likely case of the pre-allocation cache being full.
v4: Drop the pre-allocation support, we can lose the most recent fence
in case of allocation failure -- it just means we may emit more awaits
than strictly necessary but will not break.
v5: Trim allocation size for leaf nodes, they only need an array of u32
not pointers.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem_request.c            |  67 +++---
 drivers/gpu/drm/i915/i915_gem_timeline.c           | 260 +++++++++++++++++++++
 drivers/gpu/drm/i915/i915_gem_timeline.h           |  14 ++
 drivers/gpu/drm/i915/selftests/i915_gem_timeline.c | 123 ++++++++++
 .../gpu/drm/i915/selftests/i915_mock_selftests.h   |   1 +
 5 files changed, 438 insertions(+), 27 deletions(-)
 create mode 100644 drivers/gpu/drm/i915/selftests/i915_gem_timeline.c

diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index 97c07986b7c1..fb6c31ba3ef9 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -730,9 +730,7 @@ int
 i915_gem_request_await_dma_fence(struct drm_i915_gem_request *req,
 				 struct dma_fence *fence)
 {
-	struct dma_fence_array *array;
 	int ret;
-	int i;
 
 	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 		return 0;
@@ -744,39 +742,54 @@ i915_gem_request_await_dma_fence(struct drm_i915_gem_request *req,
 	if (fence->context == req->fence.context)
 		return 0;
 
-	if (dma_fence_is_i915(fence))
-		return i915_gem_request_await_request(req, to_request(fence));
+	/* Squash repeated waits to the same timelines, picking the latest */
+	if (fence->context != req->i915->mm.unordered_timeline &&
+	    intel_timeline_sync_get(req->timeline,
+				    fence->context, fence->seqno))
+		return 0;
 
-	if (!dma_fence_is_array(fence)) {
+	if (dma_fence_is_i915(fence)) {
+		ret = i915_gem_request_await_request(req, to_request(fence));
+		if (ret < 0)
+			return ret;
+	} else if (!dma_fence_is_array(fence)) {
 		ret = i915_sw_fence_await_dma_fence(&req->submit,
 						    fence, I915_FENCE_TIMEOUT,
 						    GFP_KERNEL);
-		return ret < 0 ? ret : 0;
-	}
-
-	/* Note that if the fence-array was created in signal-on-any mode,
-	 * we should *not* decompose it into its individual fences. However,
-	 * we don't currently store which mode the fence-array is operating
-	 * in. Fortunately, the only user of signal-on-any is private to
-	 * amdgpu and we should not see any incoming fence-array from
-	 * sync-file being in signal-on-any mode.
-	 */
-
-	array = to_dma_fence_array(fence);
-	for (i = 0; i < array->num_fences; i++) {
-		struct dma_fence *child = array->fences[i];
-
-		if (dma_fence_is_i915(child))
-			ret = i915_gem_request_await_request(req,
-							     to_request(child));
-		else
-			ret = i915_sw_fence_await_dma_fence(&req->submit,
-							    child, I915_FENCE_TIMEOUT,
-							    GFP_KERNEL);
 		if (ret < 0)
 			return ret;
+	} else {
+		struct dma_fence_array *array = to_dma_fence_array(fence);
+		int i;
+
+		/* Note that if the fence-array was created in signal-on-any
+		 * mode, we should *not* decompose it into its individual
+		 * fences. However, we don't currently store which mode the
+		 * fence-array is operating in. Fortunately, the only user of
+		 * signal-on-any is private to amdgpu and we should not see any
+		 * incoming fence-array from sync-file being in signal-on-any
+		 * mode.
+		 */
+
+		for (i = 0; i < array->num_fences; i++) {
+			struct dma_fence *child = array->fences[i];
+
+			if (dma_fence_is_i915(child))
+				ret = i915_gem_request_await_request(req,
+								     to_request(child));
+			else
+				ret = i915_sw_fence_await_dma_fence(&req->submit,
+								    child, I915_FENCE_TIMEOUT,
+								    GFP_KERNEL);
+			if (ret < 0)
+				return ret;
+		}
 	}
 
+	if (fence->context != req->i915->mm.unordered_timeline)
+		intel_timeline_sync_set(req->timeline,
+					fence->context, fence->seqno);
+
 	return 0;
 }
 
diff --git a/drivers/gpu/drm/i915/i915_gem_timeline.c b/drivers/gpu/drm/i915/i915_gem_timeline.c
index b596ca7ee058..f2b734dda895 100644
--- a/drivers/gpu/drm/i915/i915_gem_timeline.c
+++ b/drivers/gpu/drm/i915/i915_gem_timeline.c
@@ -24,6 +24,254 @@
 
 #include "i915_drv.h"
 
+#define NSYNC 16
+#define SHIFT ilog2(NSYNC)
+#define MASK (NSYNC - 1)
+
+/* struct intel_timeline_sync is a layer of a radixtree that maps a u64 fence
+ * context id to the last u32 fence seqno waited upon from that context.
+ * Unlike lib/radixtree it uses a parent pointer that allows traversal back to
+ * the root. This allows us to access the whole tree via a single pointer
+ * to the most recently used layer. We expect fence contexts to be dense
+ * and most reuse to be on the same i915_gem_context but on neighbouring
+ * engines (i.e. on adjacent contexts) and reuse the same leaf, a very
+ * effective lookup cache. If the new lookup is not on the same leaf, we
+ * expect it to be on the neighbouring branch.
+ *
+ * A leaf holds an array of u32 seqno, and has height 0. The bitmap field
+ * allows us to store whether a particular seqno is valid (i.e. allows us
+ * to distinguish unset from 0).
+ *
+ * A branch holds an array of layer pointers, and has height > 0, and always
+ * has at least 2 layers (either branches or leaves) below it.
+ *
+ */
+struct intel_timeline_sync {
+	u64 prefix;
+	unsigned int height;
+	unsigned int bitmap;
+	struct intel_timeline_sync *parent;
+	/* union {
+	 *	u32 seqno;
+	 *	struct intel_timeline_sync *child;
+	 * } slot[NSYNC];
+	 */
+};
+
+static inline u32 *__sync_seqno(struct intel_timeline_sync *p)
+{
+	GEM_BUG_ON(p->height);
+	return (u32 *)(p + 1);
+}
+
+static inline struct intel_timeline_sync **
+__sync_child(struct intel_timeline_sync *p)
+{
+	GEM_BUG_ON(!p->height);
+	return (struct intel_timeline_sync **)(p + 1);
+}
+
+static inline unsigned int
+__sync_idx(const struct intel_timeline_sync *p, u64 id)
+{
+	return (id >> p->height) & MASK;
+}
+
+static void __sync_free(struct intel_timeline_sync *p)
+{
+	if (p->height) {
+		unsigned int i;
+
+		while ((i = ffs(p->bitmap))) {
+			p->bitmap &= ~0u << i;
+			__sync_free(__sync_child(p)[i - 1]);
+		}
+	}
+
+	kfree(p);
+}
+
+static void sync_free(struct intel_timeline_sync *sync)
+{
+	if (!sync)
+		return;
+
+	while (sync->parent)
+		sync = sync->parent;
+
+	__sync_free(sync);
+}
+
+bool intel_timeline_sync_get(struct intel_timeline *tl, u64 id, u32 seqno)
+{
+	struct intel_timeline_sync *p;
+	unsigned int idx;
+
+	p = tl->sync;
+	if (!p)
+		return false;
+
+	if (likely((id >> SHIFT) == p->prefix))
+		goto found;
+
+	/* First climb the tree back to a parent branch */
+	do {
+		p = p->parent;
+		if (!p)
+			return false;
+
+		if ((id >> p->height >> SHIFT) == p->prefix)
+			break;
+	} while (1);
+
+	/* And then descend again until we find our leaf */
+	do {
+		if (!p->height)
+			break;
+
+		p = __sync_child(p)[__sync_idx(p, id)];
+		if (!p)
+			return false;
+
+		if ((id >> p->height >> SHIFT) != p->prefix)
+			return false;
+	} while (1);
+
+	tl->sync = p;
+found:
+	idx = id & MASK;
+	if (!(p->bitmap & BIT(idx)))
+		return false;
+
+	return i915_seqno_passed(__sync_seqno(p)[idx], seqno);
+}
+
+static noinline int
+__intel_timeline_sync_set(struct intel_timeline *tl, u64 id, u32 seqno)
+{
+	struct intel_timeline_sync *p = tl->sync;
+	unsigned int idx;
+
+	if (!p) {
+		p = kzalloc(sizeof(*p) + NSYNC * sizeof(seqno), GFP_KERNEL);
+		if (unlikely(!p))
+			return -ENOMEM;
+
+		p->prefix = id >> SHIFT;
+		goto found;
+	}
+
+	/* Climb back up the tree until we find a common prefix */
+	do {
+		if (!p->parent)
+			break;
+
+		p = p->parent;
+
+		if ((id >> p->height >> SHIFT) == p->prefix)
+			break;
+	} while (1);
+
+	/* No shortcut, we have to descend the tree to find the right layer
+	 * containing this fence.
+	 *
+	 * Each layer in the tree holds 16 (NSYNC) pointers, either fences
+	 * or lower layers. Leaf nodes (height = 0) contain the fences, all
+	 * other nodes (height > 0) are internal layers that point to a lower
+	 * node. Each internal layer has at least 2 descendents.
+	 *
+	 * Starting at the top, we check whether the current prefix matches. If
+	 * it doesn't, we have gone passed our layer and need to insert a join
+	 * into the tree, and a new leaf node as a descendent as well as the
+	 * original layer.
+	 *
+	 * The matching prefix means we are still following the right branch
+	 * of the tree. If it has height 0, we have found our leaf and just
+	 * need to replace the fence slot with ourselves. If the height is
+	 * not zero, our slot contains the next layer in the tree (unless
+	 * it is empty, in which case we can add ourselves as a new leaf).
+	 * As descend the tree the prefix grows (and height decreases).
+	 */
+	do {
+		struct intel_timeline_sync *next;
+
+		if ((id >> p->height >> SHIFT) != p->prefix) {
+			/* insert a join above the current layer */
+			next = kzalloc(sizeof(*next) + NSYNC * sizeof(next),
+				       GFP_KERNEL);
+			if (unlikely(!next))
+				return -ENOMEM;
+
+			next->height = ALIGN(fls64((id >> p->height >> SHIFT) ^ p->prefix),
+					    SHIFT) + p->height;
+			next->prefix = id >> next->height >> SHIFT;
+
+			if (p->parent)
+				__sync_child(p->parent)[__sync_idx(p->parent, id)] = next;
+			next->parent = p->parent;
+
+			idx = p->prefix >> (next->height - p->height - SHIFT) & MASK;
+			__sync_child(next)[idx] = p;
+			next->bitmap |= BIT(idx);
+			p->parent = next;
+
+			/* ascend to the join */
+			p = next;
+		} else {
+			if (!p->height)
+				break;
+		}
+
+		/* descend into the next layer */
+		GEM_BUG_ON(!p->height);
+		idx = __sync_idx(p, id);
+		next = __sync_child(p)[idx];
+		if (unlikely(!next)) {
+			next = kzalloc(sizeof(*next) + NSYNC * sizeof(seqno),
+				       GFP_KERNEL);
+			if (unlikely(!next))
+				return -ENOMEM;
+
+			__sync_child(p)[idx] = next;
+			p->bitmap |= BIT(idx);
+			next->parent = p;
+			next->prefix = id >> SHIFT;
+
+			p = next;
+			break;
+		}
+
+		p = next;
+	} while (1);
+
+found:
+	GEM_BUG_ON(p->height);
+	GEM_BUG_ON(p->prefix != id >> SHIFT);
+	tl->sync = p;
+	idx = id & MASK;
+	__sync_seqno(p)[idx] = seqno;
+	p->bitmap |= BIT(idx);
+	return 0;
+}
+
+int intel_timeline_sync_set(struct intel_timeline *tl, u64 id, u32 seqno)
+{
+	struct intel_timeline_sync *p = tl->sync;
+
+	/* We expect to be called in sequence following a  _get(id), which
+	 * should have preloaded the tl->sync hint for us.
+	 */
+	if (likely(p && (id >> SHIFT) == p->prefix)) {
+		unsigned int idx = id & MASK;
+
+		__sync_seqno(p)[idx] = seqno;
+		p->bitmap |= BIT(idx);
+		return 0;
+	}
+
+	return __intel_timeline_sync_set(tl, id, seqno);
+}
+
 static int __i915_gem_timeline_init(struct drm_i915_private *i915,
 				    struct i915_gem_timeline *timeline,
 				    const char *name,
@@ -35,6 +283,12 @@ static int __i915_gem_timeline_init(struct drm_i915_private *i915,
 
 	lockdep_assert_held(&i915->drm.struct_mutex);
 
+	/* Ideally we want a set of engines on a single leaf as we expect
+	 * to mostly be tracking synchronisation between engines.
+	 */
+	BUILD_BUG_ON(NSYNC < I915_NUM_ENGINES);
+	BUILD_BUG_ON(NSYNC > BITS_PER_BYTE * sizeof(timeline->engine[0].sync->bitmap));
+
 	timeline->i915 = i915;
 	timeline->name = kstrdup(name ?: "[kernel]", GFP_KERNEL);
 	if (!timeline->name)
@@ -91,8 +345,14 @@ void i915_gem_timeline_fini(struct i915_gem_timeline *timeline)
 		struct intel_timeline *tl = &timeline->engine[i];
 
 		GEM_BUG_ON(!list_empty(&tl->requests));
+
+		sync_free(tl->sync);
 	}
 
 	list_del(&timeline->link);
 	kfree(timeline->name);
 }
+
+#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
+#include "selftests/i915_gem_timeline.c"
+#endif
diff --git a/drivers/gpu/drm/i915/i915_gem_timeline.h b/drivers/gpu/drm/i915/i915_gem_timeline.h
index 6c53e14cab2a..c33dee0025ee 100644
--- a/drivers/gpu/drm/i915/i915_gem_timeline.h
+++ b/drivers/gpu/drm/i915/i915_gem_timeline.h
@@ -26,10 +26,13 @@
 #define I915_GEM_TIMELINE_H
 
 #include <linux/list.h>
+#include <linux/radix-tree.h>
 
+#include "i915_utils.h"
 #include "i915_gem_request.h"
 
 struct i915_gem_timeline;
+struct intel_timeline_sync;
 
 struct intel_timeline {
 	u64 fence_context;
@@ -55,6 +58,14 @@ struct intel_timeline {
 	 * struct_mutex.
 	 */
 	struct i915_gem_active last_request;
+
+	/* We track the most recent seqno that we wait on in every context so
+	 * that we only have to emit a new await and dependency on a more
+	 * recent sync point. As the contexts may executed out-of-order, we
+	 * have to track each individually and cannot not rely on an absolute
+	 * global_seqno.
+	 */
+	struct intel_timeline_sync *sync;
 	u32 sync_seqno[I915_NUM_ENGINES];
 
 	struct i915_gem_timeline *common;
@@ -75,4 +86,7 @@ int i915_gem_timeline_init(struct drm_i915_private *i915,
 int i915_gem_timeline_init__global(struct drm_i915_private *i915);
 void i915_gem_timeline_fini(struct i915_gem_timeline *tl);
 
+bool intel_timeline_sync_get(struct intel_timeline *tl, u64 id, u32 seqno);
+int intel_timeline_sync_set(struct intel_timeline *tl, u64 id, u32 seqno);
+
 #endif
diff --git a/drivers/gpu/drm/i915/selftests/i915_gem_timeline.c b/drivers/gpu/drm/i915/selftests/i915_gem_timeline.c
new file mode 100644
index 000000000000..c0bb8ecac93b
--- /dev/null
+++ b/drivers/gpu/drm/i915/selftests/i915_gem_timeline.c
@@ -0,0 +1,123 @@
+/*
+ * Copyright © 2017 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.
+ *
+ */
+
+#include "../i915_selftest.h"
+#include "mock_gem_device.h"
+
+static int igt_seqmap(void *arg)
+{
+	struct drm_i915_private *i915 = arg;
+	const struct {
+		const char *name;
+		u32 seqno;
+		bool expected;
+		bool set;
+	} pass[] = {
+		{ "unset", 0, false, false },
+		{ "new", 0, false, true },
+		{ "0a", 0, true, true },
+		{ "1a", 1, false, true },
+		{ "1b", 1, true, true },
+		{ "0b", 0, true, false },
+		{ "2a", 2, false, true },
+		{ "4", 4, false, true },
+		{ "INT_MAX", INT_MAX, false, true },
+		{ "INT_MAX-1", INT_MAX-1, true, false },
+		{ "INT_MAX+1", (u32)INT_MAX+1, false, true },
+		{ "INT_MAX", INT_MAX, true, false },
+		{ "UINT_MAX", UINT_MAX, false, true },
+		{ "wrap", 0, false, true },
+		{ "unwrap", UINT_MAX, true, false },
+		{},
+	}, *p;
+	struct intel_timeline *tl;
+	int order, offset;
+	int ret;
+
+	tl = &i915->gt.global_timeline.engine[RCS];
+	for (p = pass; p->name; p++) {
+		for (order = 1; order < 64; order++) {
+			for (offset = -1; offset <= (order > 1); offset++) {
+				u64 ctx = BIT_ULL(order) + offset;
+
+				if (intel_timeline_sync_get(tl,
+							    ctx,
+							    p->seqno) != p->expected) {
+					pr_err("1: %s(ctx=%llu, seqno=%u) expected passed %s but failed\n",
+					       p->name, ctx, p->seqno, yesno(p->expected));
+					return -EINVAL;
+				}
+
+				if (p->set) {
+					ret = intel_timeline_sync_set(tl, ctx, p->seqno);
+					if (ret)
+						return ret;
+				}
+			}
+		}
+	}
+
+	tl = &i915->gt.global_timeline.engine[BCS];
+	for (order = 1; order < 64; order++) {
+		for (offset = -1; offset <= (order > 1); offset++) {
+			u64 ctx = BIT_ULL(order) + offset;
+
+			for (p = pass; p->name; p++) {
+				if (intel_timeline_sync_get(tl,
+							    ctx,
+							    p->seqno) != p->expected) {
+					pr_err("2: %s(ctx=%llu, seqno=%u) expected passed %s but failed\n",
+					       p->name, ctx, p->seqno, yesno(p->expected));
+					return -EINVAL;
+				}
+
+				if (p->set) {
+					ret = intel_timeline_sync_set(tl, ctx, p->seqno);
+					if (ret)
+						return ret;
+				}
+			}
+		}
+	}
+
+	return 0;
+}
+
+int i915_gem_timeline_mock_selftests(void)
+{
+	static const struct i915_subtest tests[] = {
+		SUBTEST(igt_seqmap),
+	};
+	struct drm_i915_private *i915;
+	int err;
+
+	i915 = mock_gem_device();
+	if (!i915)
+		return -ENOMEM;
+
+	err = i915_subtests(tests, i915);
+	drm_dev_unref(&i915->drm);
+
+	return err;
+}
diff --git a/drivers/gpu/drm/i915/selftests/i915_mock_selftests.h b/drivers/gpu/drm/i915/selftests/i915_mock_selftests.h
index be9a9ebf5692..8d0f50c25df8 100644
--- a/drivers/gpu/drm/i915/selftests/i915_mock_selftests.h
+++ b/drivers/gpu/drm/i915/selftests/i915_mock_selftests.h
@@ -12,6 +12,7 @@ selftest(sanitycheck, i915_mock_sanitycheck) /* keep first (igt selfcheck) */
 selftest(scatterlist, scatterlist_mock_selftests)
 selftest(uncore, intel_uncore_mock_selftests)
 selftest(breadcrumbs, intel_breadcrumbs_mock_selftests)
+selftest(timelines, i915_gem_timeline_mock_selftests)
 selftest(requests, i915_gem_request_mock_selftests)
 selftest(objects, i915_gem_object_mock_selftests)
 selftest(dmabuf, i915_gem_dmabuf_mock_selftests)
-- 
2.11.0



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