[PATCH 21/80] drm/i915: Reduce context HW ID lifetime

Chris Wilson chris at chris-wilson.co.uk
Thu Aug 2 10:28:26 UTC 2018


Future gen reduce the number of bits we will have available to
differentiate between contexts, so reduce the lifetime of the ID
assignment from that of the context to its current active cycle (i.e.
only while it is pinned for use by the HW, will it have a constant ID).
This means that instead of a max of 2k allocated contexts (worst case
before fun with bit twiddling), we instead have a limit of 2k in flight
contexts (minus a few that have been pinned by the kernel or by perf).

We cannot reduce the scope of an HW-ID to an engine (allowing the same
gem_context to have different ids on each engine) as in the future we
will need to preassign an id before we know which engine the
context is being executed on.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
Cc: Oscar Mateo <oscar.mateo at intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
Cc: Michel Thierry <michel.thierry at intel.com>
---
 drivers/gpu/drm/i915/i915_debugfs.c           |   5 +-
 drivers/gpu/drm/i915/i915_drv.h               |   2 +
 drivers/gpu/drm/i915/i915_gem_context.c       | 207 +++++++++++++-----
 drivers/gpu/drm/i915/i915_gem_context.h       |  17 ++
 drivers/gpu/drm/i915/intel_lrc.c              |   8 +
 drivers/gpu/drm/i915/selftests/mock_context.c |  11 +-
 6 files changed, 181 insertions(+), 69 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 68dc07611f2c..4bcccdd95ab4 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -1950,7 +1950,10 @@ static int i915_context_status(struct seq_file *m, void *unused)
 		return ret;
 
 	list_for_each_entry(ctx, &dev_priv->contexts.list, link) {
-		seq_printf(m, "HW context %u ", ctx->hw_id);
+		seq_puts(m, "HW context ");
+		if (!list_empty(&ctx->hw_id_link))
+			seq_printf(m, "%x [pin %u]",
+				   ctx->hw_id, atomic_read(&ctx->pin_hw_id));
 		if (ctx->pid) {
 			struct task_struct *task;
 
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 1d72d5b94e4e..002134f9a0d2 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1821,6 +1821,7 @@ struct drm_i915_private {
 	struct mutex av_mutex;
 
 	struct {
+		struct mutex mutex;
 		struct list_head list;
 		struct llist_head free_list;
 		struct work_struct free_work;
@@ -1833,6 +1834,7 @@ struct drm_i915_private {
 #define MAX_CONTEXT_HW_ID (1<<21) /* exclusive */
 #define MAX_GUC_CONTEXT_HW_ID (1 << 20) /* exclusive */
 #define GEN11_MAX_CONTEXT_HW_ID (1<<11) /* exclusive */
+		struct list_head hw_id_list;
 	} contexts;
 
 	u32 fdi_rx_config;
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index f15a039772db..d3390942f37b 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -115,6 +115,85 @@ static void lut_close(struct i915_gem_context *ctx)
 	rcu_read_unlock();
 }
 
+static inline int new_hw_id(struct drm_i915_private *i915, gfp_t gfp)
+{
+	unsigned int max;
+
+	lockdep_assert_held(&i915->contexts.mutex);
+
+	if (INTEL_GEN(i915) >= 11)
+		max = GEN11_MAX_CONTEXT_HW_ID;
+	else if (USES_GUC_SUBMISSION(i915))
+		/*
+		 * When using GuC in proxy submission, GuC consumes the
+		 * highest bit in the context id to indicate proxy submission.
+		 */
+		max = MAX_GUC_CONTEXT_HW_ID;
+	else
+		max = MAX_CONTEXT_HW_ID;
+
+	return ida_simple_get(&i915->contexts.hw_ida, 0, max, gfp);
+}
+
+static int steal_hw_id(struct drm_i915_private *i915)
+{
+	struct i915_gem_context *ctx, *cn;
+	LIST_HEAD(pinned);
+	int id = -ENOSPC;
+
+	lockdep_assert_held(&i915->contexts.mutex);
+
+	list_for_each_entry_safe(ctx, cn,
+				 &i915->contexts.hw_id_list, hw_id_link) {
+		if (atomic_read(&ctx->pin_hw_id)) {
+			list_move_tail(&ctx->hw_id_link, &pinned);
+			continue;
+		}
+
+		GEM_BUG_ON(!ctx->hw_id); /* perma-pinned kernel context */
+		list_del_init(&ctx->hw_id_link);
+		id = ctx->hw_id;
+		break;
+	}
+
+	list_splice_tail(&pinned, &i915->contexts.hw_id_list);
+	return id;
+}
+
+static int assign_hw_id(struct drm_i915_private *i915, unsigned int *out)
+{
+	int ret;
+
+	lockdep_assert_held(&i915->contexts.mutex);
+
+	ret = new_hw_id(i915, GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
+	if (unlikely(ret < 0)) {
+		ret = steal_hw_id(i915);
+		if (ret < 0) /* once again for the correct erro code */
+			ret = new_hw_id(i915, GFP_KERNEL);
+		if (ret < 0)
+			return ret;
+	}
+
+	*out = ret;
+	return 0;
+}
+
+static void release_hw_id(struct i915_gem_context *ctx)
+{
+	struct drm_i915_private *i915 = ctx->i915;
+
+	if (list_empty(&ctx->hw_id_link))
+		return;
+
+	mutex_lock(&i915->contexts.mutex);
+	if (!list_empty(&ctx->hw_id_link)) {
+		ida_simple_remove(&i915->contexts.hw_ida, ctx->hw_id);
+		list_del_init(&ctx->hw_id_link);
+	}
+	mutex_unlock(&i915->contexts.mutex);
+}
+
 static void i915_gem_context_free(struct i915_gem_context *ctx)
 {
 	unsigned int n;
@@ -122,6 +201,7 @@ static void i915_gem_context_free(struct i915_gem_context *ctx)
 	lockdep_assert_held(&ctx->i915->drm.struct_mutex);
 	GEM_BUG_ON(!i915_gem_context_is_closed(ctx));
 
+	release_hw_id(ctx);
 	i915_ppgtt_put(ctx->ppgtt);
 
 	for (n = 0; n < ARRAY_SIZE(ctx->__engine); n++) {
@@ -136,7 +216,6 @@ static void i915_gem_context_free(struct i915_gem_context *ctx)
 
 	list_del(&ctx->link);
 
-	ida_simple_remove(&ctx->i915->contexts.hw_ida, ctx->hw_id);
 	kfree_rcu(ctx, rcu);
 }
 
@@ -190,6 +269,12 @@ static void context_close(struct i915_gem_context *ctx)
 {
 	i915_gem_context_set_closed(ctx);
 
+	/*
+	 * This context will never again be assinged to HW, so we can
+	 * reuse its ID for the next context.
+	 */
+	release_hw_id(ctx);
+
 	/*
 	 * The LUT uses the VMA as a backpointer to unref the object,
 	 * so we need to clear the LUT before we close all the VMA (inside
@@ -203,43 +288,6 @@ static void context_close(struct i915_gem_context *ctx)
 	i915_gem_context_put(ctx);
 }
 
-static int assign_hw_id(struct drm_i915_private *dev_priv, unsigned *out)
-{
-	int ret;
-	unsigned int max;
-
-	if (INTEL_GEN(dev_priv) >= 11) {
-		max = GEN11_MAX_CONTEXT_HW_ID;
-	} else {
-		/*
-		 * When using GuC in proxy submission, GuC consumes the
-		 * highest bit in the context id to indicate proxy submission.
-		 */
-		if (USES_GUC_SUBMISSION(dev_priv))
-			max = MAX_GUC_CONTEXT_HW_ID;
-		else
-			max = MAX_CONTEXT_HW_ID;
-	}
-
-
-	ret = ida_simple_get(&dev_priv->contexts.hw_ida,
-			     0, max, GFP_KERNEL);
-	if (ret < 0) {
-		/* Contexts are only released when no longer active.
-		 * Flush any pending retires to hopefully release some
-		 * stale contexts and try again.
-		 */
-		i915_retire_requests(dev_priv);
-		ret = ida_simple_get(&dev_priv->contexts.hw_ida,
-				     0, max, GFP_KERNEL);
-		if (ret < 0)
-			return ret;
-	}
-
-	*out = ret;
-	return 0;
-}
-
 static u32 default_desc_template(const struct drm_i915_private *i915,
 				 const struct i915_hw_ppgtt *ppgtt)
 {
@@ -276,12 +324,6 @@ __create_hw_context(struct drm_i915_private *dev_priv,
 	if (ctx == NULL)
 		return ERR_PTR(-ENOMEM);
 
-	ret = assign_hw_id(dev_priv, &ctx->hw_id);
-	if (ret) {
-		kfree(ctx);
-		return ERR_PTR(ret);
-	}
-
 	kref_init(&ctx->ref);
 	list_add_tail(&ctx->link, &dev_priv->contexts.list);
 	ctx->i915 = dev_priv;
@@ -295,6 +337,7 @@ __create_hw_context(struct drm_i915_private *dev_priv,
 
 	INIT_RADIX_TREE(&ctx->handles_vma, GFP_KERNEL);
 	INIT_LIST_HEAD(&ctx->handles_list);
+	INIT_LIST_HEAD(&ctx->hw_id_link);
 
 	/* Default context will never have a file_priv */
 	ret = DEFAULT_CONTEXT_HANDLE;
@@ -421,15 +464,35 @@ i915_gem_context_create_gvt(struct drm_device *dev)
 	return ctx;
 }
 
+static void
+destroy_kernel_context(struct i915_gem_context **ctxp)
+{
+	struct i915_gem_context *ctx;
+
+	/* Keep the context ref so that we can free it immediately ourselves */
+	ctx = i915_gem_context_get(fetch_and_zero(ctxp));
+	GEM_BUG_ON(!i915_gem_context_is_kernel(ctx));
+
+	context_close(ctx);
+	i915_gem_context_free(ctx);
+}
+
 struct i915_gem_context *
 i915_gem_context_create_kernel(struct drm_i915_private *i915, int prio)
 {
 	struct i915_gem_context *ctx;
+	int err;
 
 	ctx = i915_gem_create_context(i915, NULL);
 	if (IS_ERR(ctx))
 		return ctx;
 
+	err = i915_gem_context_pin_hw_id(ctx);
+	if (err) {
+		destroy_kernel_context(&ctx);
+		return ERR_PTR(err);
+	}
+
 	i915_gem_context_clear_bannable(ctx);
 	ctx->sched.priority = prio;
 	ctx->ring_size = PAGE_SIZE;
@@ -439,17 +502,19 @@ i915_gem_context_create_kernel(struct drm_i915_private *i915, int prio)
 	return ctx;
 }
 
-static void
-destroy_kernel_context(struct i915_gem_context **ctxp)
+static void init_contexts(struct drm_i915_private *i915)
 {
-	struct i915_gem_context *ctx;
+	mutex_init(&i915->contexts.mutex);
+	INIT_LIST_HEAD(&i915->contexts.list);
 
-	/* Keep the context ref so that we can free it immediately ourselves */
-	ctx = i915_gem_context_get(fetch_and_zero(ctxp));
-	GEM_BUG_ON(!i915_gem_context_is_kernel(ctx));
+	/* Using the simple ida interface, the max is limited by sizeof(int) */
+	BUILD_BUG_ON(MAX_CONTEXT_HW_ID > INT_MAX);
+	BUILD_BUG_ON(GEN11_MAX_CONTEXT_HW_ID > INT_MAX);
+	ida_init(&i915->contexts.hw_ida);
+	INIT_LIST_HEAD(&i915->contexts.hw_id_list);
 
-	context_close(ctx);
-	i915_gem_context_free(ctx);
+	INIT_WORK(&i915->contexts.free_work, contexts_free_worker);
+	init_llist_head(&i915->contexts.free_list);
 }
 
 static bool needs_preempt_context(struct drm_i915_private *i915)
@@ -470,14 +535,7 @@ int i915_gem_contexts_init(struct drm_i915_private *dev_priv)
 	if (ret)
 		return ret;
 
-	INIT_LIST_HEAD(&dev_priv->contexts.list);
-	INIT_WORK(&dev_priv->contexts.free_work, contexts_free_worker);
-	init_llist_head(&dev_priv->contexts.free_list);
-
-	/* Using the simple ida interface, the max is limited by sizeof(int) */
-	BUILD_BUG_ON(MAX_CONTEXT_HW_ID > INT_MAX);
-	BUILD_BUG_ON(GEN11_MAX_CONTEXT_HW_ID > INT_MAX);
-	ida_init(&dev_priv->contexts.hw_ida);
+	init_contexts(dev_priv);
 
 	/* lowest priority; idle task */
 	ctx = i915_gem_context_create_kernel(dev_priv, I915_PRIORITY_MIN);
@@ -490,6 +548,7 @@ int i915_gem_contexts_init(struct drm_i915_private *dev_priv)
 	 * all user contexts will have non-zero hw_id.
 	 */
 	GEM_BUG_ON(ctx->hw_id);
+	GEM_BUG_ON(!atomic_read(&ctx->pin_hw_id));
 	dev_priv->kernel_context = ctx;
 
 	/* highest priority; preempting task */
@@ -527,6 +586,7 @@ void i915_gem_contexts_fini(struct drm_i915_private *i915)
 	destroy_kernel_context(&i915->kernel_context);
 
 	/* Must free all deferred contexts (via flush_workqueue) first */
+	GEM_BUG_ON(!list_empty(&i915->contexts.hw_id_list));
 	ida_destroy(&i915->contexts.hw_ida);
 }
 
@@ -932,6 +992,33 @@ int i915_gem_context_reset_stats_ioctl(struct drm_device *dev,
 	return ret;
 }
 
+int __i915_gem_context_pin_hw_id(struct i915_gem_context *ctx)
+{
+	struct drm_i915_private *i915 = ctx->i915;
+	int err = 0;
+
+	mutex_lock(&i915->contexts.mutex);
+
+	GEM_BUG_ON(i915_gem_context_is_closed(ctx));
+
+	if (list_empty(&ctx->hw_id_link)) {
+		GEM_BUG_ON(atomic_read(&ctx->pin_hw_id));
+
+		err = assign_hw_id(i915, &ctx->hw_id);
+		if (err)
+			goto out_unlock;
+
+		list_add_tail(&ctx->hw_id_link, &i915->contexts.hw_id_list);
+	}
+
+	GEM_BUG_ON(atomic_read(&ctx->pin_hw_id) == ~0u);
+	atomic_inc(&ctx->pin_hw_id);
+
+out_unlock:
+	mutex_unlock(&i915->contexts.mutex);
+	return err;
+}
+
 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
 #include "selftests/mock_context.c"
 #include "selftests/i915_gem_context.c"
diff --git a/drivers/gpu/drm/i915/i915_gem_context.h b/drivers/gpu/drm/i915/i915_gem_context.h
index 851dad6decd7..c73ac614f58c 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.h
+++ b/drivers/gpu/drm/i915/i915_gem_context.h
@@ -136,6 +136,8 @@ struct i915_gem_context {
 	 * id for the lifetime of the context.
 	 */
 	unsigned int hw_id;
+	atomic_t pin_hw_id;
+	struct list_head hw_id_link;
 
 	/**
 	 * @user_handle: userspace identifier
@@ -254,6 +256,21 @@ static inline void i915_gem_context_set_force_single_submission(struct i915_gem_
 	__set_bit(CONTEXT_FORCE_SINGLE_SUBMISSION, &ctx->flags);
 }
 
+int __i915_gem_context_pin_hw_id(struct i915_gem_context *ctx);
+static inline int i915_gem_context_pin_hw_id(struct i915_gem_context *ctx)
+{
+	if (atomic_inc_not_zero(&ctx->pin_hw_id))
+		return 0;
+
+	return __i915_gem_context_pin_hw_id(ctx);
+}
+
+static inline void i915_gem_context_unpin_hw_id(struct i915_gem_context *ctx)
+{
+	GEM_BUG_ON(atomic_read(&ctx->pin_hw_id) == 0u);
+	atomic_dec(&ctx->pin_hw_id);
+}
+
 static inline bool i915_gem_context_is_default(const struct i915_gem_context *c)
 {
 	return c->user_handle == DEFAULT_CONTEXT_HANDLE;
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index a6ce18954440..b567931878f1 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1283,6 +1283,8 @@ static void execlists_context_destroy(struct intel_context *ce)
 
 static void execlists_context_unpin(struct intel_context *ce)
 {
+	i915_gem_context_unpin_hw_id(ce->gem_context);
+
 	intel_ring_unpin(ce->ring);
 
 	ce->state->obj->pin_global--;
@@ -1341,6 +1343,10 @@ __execlists_context_pin(struct intel_engine_cs *engine,
 	if (ret)
 		goto unpin_map;
 
+	ret = i915_gem_context_pin_hw_id(ctx);
+	if (ret)
+		goto unpin_ring;
+
 	intel_lr_context_descriptor_update(ctx, engine, ce);
 
 	ce->lrc_reg_state = vaddr + LRC_STATE_PN * PAGE_SIZE;
@@ -1353,6 +1359,8 @@ __execlists_context_pin(struct intel_engine_cs *engine,
 	i915_gem_context_get(ctx);
 	return ce;
 
+unpin_ring:
+	intel_ring_unpin(ce->ring);
 unpin_map:
 	i915_gem_object_unpin_map(ce->state->obj);
 unpin_vma:
diff --git a/drivers/gpu/drm/i915/selftests/mock_context.c b/drivers/gpu/drm/i915/selftests/mock_context.c
index 8904f1ce64e3..d937bdff26f9 100644
--- a/drivers/gpu/drm/i915/selftests/mock_context.c
+++ b/drivers/gpu/drm/i915/selftests/mock_context.c
@@ -43,6 +43,7 @@ mock_context(struct drm_i915_private *i915,
 
 	INIT_RADIX_TREE(&ctx->handles_vma, GFP_KERNEL);
 	INIT_LIST_HEAD(&ctx->handles_list);
+	INIT_LIST_HEAD(&ctx->hw_id_link);
 
 	for (n = 0; n < ARRAY_SIZE(ctx->__engine); n++) {
 		struct intel_context *ce = &ctx->__engine[n];
@@ -50,11 +51,9 @@ mock_context(struct drm_i915_private *i915,
 		ce->gem_context = ctx;
 	}
 
-	ret = ida_simple_get(&i915->contexts.hw_ida,
-			     0, MAX_CONTEXT_HW_ID, GFP_KERNEL);
+	ret = i915_gem_context_pin_hw_id(ctx);
 	if (ret < 0)
 		goto err_handles;
-	ctx->hw_id = ret;
 
 	if (name) {
 		ctx->name = kstrdup(name, GFP_KERNEL);
@@ -85,11 +84,7 @@ void mock_context_close(struct i915_gem_context *ctx)
 
 void mock_init_contexts(struct drm_i915_private *i915)
 {
-	INIT_LIST_HEAD(&i915->contexts.list);
-	ida_init(&i915->contexts.hw_ida);
-
-	INIT_WORK(&i915->contexts.free_work, contexts_free_worker);
-	init_llist_head(&i915->contexts.free_list);
+	init_contexts(i915);
 }
 
 struct i915_gem_context *
-- 
2.18.0



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