Re: [PATCH 10/26] drm/i915/guc: Assign contexts in parent-child relationship consecutive guc_ids

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On 10/7/2021 18:21, Matthew Brost wrote:
On Thu, Oct 07, 2021 at 03:03:04PM -0700, John Harrison wrote:
On 10/4/2021 15:06, Matthew Brost wrote:
Assign contexts in parent-child relationship consecutive guc_ids. This
is accomplished by partitioning guc_id space between ones that need to
be consecutive (1/16 available guc_ids) and ones that do not (15/16 of
available guc_ids). The consecutive search is implemented via the bitmap
API.

This is a precursor to the full GuC multi-lrc implementation but aligns
to how GuC mutli-lrc interface is defined - guc_ids must be consecutive
when using the GuC multi-lrc interface.

v2:
   (Daniel Vetter)
    - Explicitly state why we assign consecutive guc_ids
v3:
   (John Harrison)
    - Bring back in spin lock

Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
---
   drivers/gpu/drm/i915/gt/uc/intel_guc.h        |   6 +-
   .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 104 ++++++++++++++----
   2 files changed, 86 insertions(+), 24 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
index 25a598e2b6e8..a9f4ec972bfb 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
@@ -76,9 +76,13 @@ struct intel_guc {
   		 */
   		spinlock_t lock;
   		/**
-		 * @guc_ids: used to allocate new guc_ids
+		 * @guc_ids: used to allocate new guc_ids, single-lrc
   		 */
   		struct ida guc_ids;
+		/**
+		 * @guc_ids_bitmap: used to allocate new guc_ids, multi-lrc
+		 */
+		unsigned long *guc_ids_bitmap;
   		/**
   		 * @guc_id_list: list of intel_context with valid guc_ids but no
   		 * refs
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index 1f2809187513..79e7732e83b2 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -128,6 +128,16 @@ guc_create_virtual(struct intel_engine_cs **siblings, unsigned int count);
   #define GUC_REQUEST_SIZE 64 /* bytes */
+/*
+ * We reserve 1/16 of the guc_ids for multi-lrc as these need to be contiguous
+ * per the GuC submission interface. A different allocation algorithm is used
+ * (bitmap vs. ida) between multi-lrc and single-lrc hence the reason to
+ * partition the guc_id space. We believe the number of multi-lrc contexts in
+ * use should be low and 1/16 should be sufficient. Minimum of 32 guc_ids for
+ * multi-lrc.
+ */
+#define NUMBER_MULTI_LRC_GUC_ID		(GUC_MAX_LRC_DESCRIPTORS / 16)
+
   /*
    * Below is a set of functions which control the GuC scheduling state which
    * require a lock.
@@ -1206,6 +1216,11 @@ int intel_guc_submission_init(struct intel_guc *guc)
   	INIT_WORK(&guc->submission_state.destroyed_worker,
   		  destroyed_worker_func);
+	guc->submission_state.guc_ids_bitmap =
+		bitmap_zalloc(NUMBER_MULTI_LRC_GUC_ID, GFP_KERNEL);
+	if (!guc->submission_state.guc_ids_bitmap)
+		return -ENOMEM;
+
   	return 0;
   }
@@ -1217,6 +1232,7 @@ void intel_guc_submission_fini(struct intel_guc *guc)
   	guc_lrc_desc_pool_destroy(guc);
   	guc_flush_destroyed_contexts(guc);
   	i915_sched_engine_put(guc->sched_engine);
+	bitmap_free(guc->submission_state.guc_ids_bitmap);
   }
   static inline void queue_request(struct i915_sched_engine *sched_engine,
@@ -1268,18 +1284,43 @@ static void guc_submit_request(struct i915_request *rq)
   	spin_unlock_irqrestore(&sched_engine->lock, flags);
   }
-static int new_guc_id(struct intel_guc *guc)
+static int new_guc_id(struct intel_guc *guc, struct intel_context *ce)
   {
-	return ida_simple_get(&guc->submission_state.guc_ids, 0,
-			      GUC_MAX_LRC_DESCRIPTORS, GFP_KERNEL |
-			      __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
+	int ret;
+
+	GEM_BUG_ON(intel_context_is_child(ce));
+
+	if (intel_context_is_parent(ce))
+		ret = bitmap_find_free_region(guc->submission_state.guc_ids_bitmap,
+					      NUMBER_MULTI_LRC_GUC_ID,
+					      order_base_2(ce->parallel.number_children
+							   + 1));
+	else
+		ret = ida_simple_get(&guc->submission_state.guc_ids,
+				     NUMBER_MULTI_LRC_GUC_ID,
+				     GUC_MAX_LRC_DESCRIPTORS,
+				     GFP_KERNEL | __GFP_RETRY_MAYFAIL |
+				     __GFP_NOWARN);
+	if (unlikely(ret < 0))
+		return ret;
+
+	ce->guc_id.id = ret;
+	return 0;
   }
   static void __release_guc_id(struct intel_guc *guc, struct intel_context *ce)
   {
+	GEM_BUG_ON(intel_context_is_child(ce));
+
   	if (!context_guc_id_invalid(ce)) {
-		ida_simple_remove(&guc->submission_state.guc_ids,
-				  ce->guc_id.id);
+		if (intel_context_is_parent(ce))
+			bitmap_release_region(guc->submission_state.guc_ids_bitmap,
+					      ce->guc_id.id,
+					      order_base_2(ce->parallel.number_children
+							   + 1));
There was a discussion on the previous revision about adding a BUG_ON to
ensure that number_children cannot change between the bitmap alloc and the
bitmap release. I'm not seeing the new BUG_ON mentioned in this patch.

I thought you meant to add a BUG_ON to ensure before we release a region
/ id it is occupied? I looked in both the bitmap API and ida API and
neither have a function that checks if region / id is occupied so can't
really add a BUG_ON for that.

How much you add BUG_ON to ensure the number of children canoot change
between alloc and release? I don't follow how that would work.

Matt
I was thinking that where number_children is modified, you have a BUG_ON(guc_id_is_valid). That would ensure that the release has to match the alloc. Hmm, you already have a BUG_ON about the parent/child not being pinned in intel_context_bind_parent_child(), which I guess covers it because you shouldn't have a guc_id if you aren't pinned, right? And that is the only function which can modify number_children, yes? So maybe it's all good?

John.


John.


+		else
+			ida_simple_remove(&guc->submission_state.guc_ids,
+					  ce->guc_id.id);
   		reset_lrc_desc(guc, ce->guc_id.id);
   		set_context_guc_id_invalid(ce);
   	}
@@ -1296,49 +1337,64 @@ static void release_guc_id(struct intel_guc *guc, struct intel_context *ce)
   	spin_unlock_irqrestore(&guc->submission_state.lock, flags);
   }
-static int steal_guc_id(struct intel_guc *guc)
+static int steal_guc_id(struct intel_guc *guc, struct intel_context *ce)
   {
-	struct intel_context *ce;
-	int guc_id;
+	struct intel_context *cn;
   	lockdep_assert_held(&guc->submission_state.lock);
+	GEM_BUG_ON(intel_context_is_child(ce));
+	GEM_BUG_ON(intel_context_is_parent(ce));
   	if (!list_empty(&guc->submission_state.guc_id_list)) {
-		ce = list_first_entry(&guc->submission_state.guc_id_list,
+		cn = list_first_entry(&guc->submission_state.guc_id_list,
   				      struct intel_context,
   				      guc_id.link);
-		GEM_BUG_ON(atomic_read(&ce->guc_id.ref));
-		GEM_BUG_ON(context_guc_id_invalid(ce));
+		GEM_BUG_ON(atomic_read(&cn->guc_id.ref));
+		GEM_BUG_ON(context_guc_id_invalid(cn));
+		GEM_BUG_ON(intel_context_is_child(cn));
+		GEM_BUG_ON(intel_context_is_parent(cn));
-		list_del_init(&ce->guc_id.link);
-		guc_id = ce->guc_id.id;
+		list_del_init(&cn->guc_id.link);
+		ce->guc_id = cn->guc_id;
   		spin_lock(&ce->guc_state.lock);
-		clr_context_registered(ce);
+		clr_context_registered(cn);
   		spin_unlock(&ce->guc_state.lock);
-		set_context_guc_id_invalid(ce);
-		return guc_id;
+		set_context_guc_id_invalid(cn);
+
+		return 0;
   	} else {
   		return -EAGAIN;
   	}
   }
-static int assign_guc_id(struct intel_guc *guc, u16 *out)
+static int assign_guc_id(struct intel_guc *guc, struct intel_context *ce)
   {
   	int ret;
   	lockdep_assert_held(&guc->submission_state.lock);
+	GEM_BUG_ON(intel_context_is_child(ce));
-	ret = new_guc_id(guc);
+	ret = new_guc_id(guc, ce);
   	if (unlikely(ret < 0)) {
-		ret = steal_guc_id(guc);
+		if (intel_context_is_parent(ce))
+			return -ENOSPC;
+
+		ret = steal_guc_id(guc, ce);
   		if (ret < 0)
   			return ret;
   	}
-	*out = ret;
+	if (intel_context_is_parent(ce)) {
+		struct intel_context *child;
+		int i = 1;
+
+		for_each_child(ce, child)
+			child->guc_id.id = ce->guc_id.id + i++;
+	}
+
   	return 0;
   }
@@ -1356,7 +1412,7 @@ static int pin_guc_id(struct intel_guc *guc, struct intel_context *ce)
   	might_lock(&ce->guc_state.lock);
   	if (context_guc_id_invalid(ce)) {
-		ret = assign_guc_id(guc, &ce->guc_id.id);
+		ret = assign_guc_id(guc, ce);
   		if (ret)
   			goto out_unlock;
   		ret = 1;	/* Indidcates newly assigned guc_id */
@@ -1398,8 +1454,10 @@ static void unpin_guc_id(struct intel_guc *guc, struct intel_context *ce)
   	unsigned long flags;
   	GEM_BUG_ON(atomic_read(&ce->guc_id.ref) < 0);
+	GEM_BUG_ON(intel_context_is_child(ce));
-	if (unlikely(context_guc_id_invalid(ce)))
+	if (unlikely(context_guc_id_invalid(ce) ||
+		     intel_context_is_parent(ce)))
   		return;
   	spin_lock_irqsave(&guc->submission_state.lock, flags);




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