[Intel-gfx] [PATCH] drm/i915/guc: Use lockless list for destroyed contexts

[Matthew Brost]

Use a lockless list structure for destroyed contexts to avoid hammering
on global submission spin lock.

Suggested-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Signed-off-by: Matthew Brost <matthew.brost at intel.com>
---
 drivers/gpu/drm/i915/gt/intel_context.c       |  2 -
 drivers/gpu/drm/i915/gt/intel_context_types.h |  3 +-
 drivers/gpu/drm/i915/gt/uc/intel_guc.h        |  3 +-
 .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 44 +++++--------------
 4 files changed, 16 insertions(+), 36 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
index 5d0ec7c49b6a..4aacb4b0418d 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.c
+++ b/drivers/gpu/drm/i915/gt/intel_context.c
@@ -403,8 +403,6 @@ intel_context_init(struct intel_context *ce, struct intel_engine_cs *engine)
 	ce->guc_id.id = GUC_INVALID_LRC_ID;
 	INIT_LIST_HEAD(&ce->guc_id.link);
 
-	INIT_LIST_HEAD(&ce->destroyed_link);
-
 	INIT_LIST_HEAD(&ce->parallel.child_list);
 
 	/*
diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
index 30cd81ad8911..4532d43ec9c0 100644
--- a/drivers/gpu/drm/i915/gt/intel_context_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
@@ -9,6 +9,7 @@
 #include <linux/average.h>
 #include <linux/kref.h>
 #include <linux/list.h>
+#include <linux/llist.h>
 #include <linux/mutex.h>
 #include <linux/types.h>
 
@@ -224,7 +225,7 @@ struct intel_context {
 	 * list when context is pending to be destroyed (deregistered with the
 	 * GuC), protected by guc->submission_state.lock
 	 */
-	struct list_head destroyed_link;
+	struct llist_node destroyed_link;
 
 	/** @parallel: sub-structure for parallel submission members */
 	struct {
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
index f9240d4baa69..705085058411 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
@@ -8,6 +8,7 @@
 
 #include <linux/xarray.h>
 #include <linux/delay.h>
+#include <linux/llist.h>
 
 #include "intel_uncore.h"
 #include "intel_guc_fw.h"
@@ -112,7 +113,7 @@ struct intel_guc {
 		 * @destroyed_contexts: list of contexts waiting to be destroyed
 		 * (deregistered with the GuC)
 		 */
-		struct list_head destroyed_contexts;
+		struct llist_head destroyed_contexts;
 		/**
 		 * @destroyed_worker: worker to deregister contexts, need as we
 		 * need to take a GT PM reference and can't from destroy
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 0a03a30e4c6d..6f7643edc139 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -1771,7 +1771,7 @@ int intel_guc_submission_init(struct intel_guc *guc)
 	spin_lock_init(&guc->submission_state.lock);
 	INIT_LIST_HEAD(&guc->submission_state.guc_id_list);
 	ida_init(&guc->submission_state.guc_ids);
-	INIT_LIST_HEAD(&guc->submission_state.destroyed_contexts);
+	init_llist_head(&guc->submission_state.destroyed_contexts);
 	INIT_WORK(&guc->submission_state.destroyed_worker,
 		  destroyed_worker_func);
 
@@ -2696,26 +2696,18 @@ static void __guc_context_destroy(struct intel_context *ce)
 	}
 }
 
+#define take_destroyed_contexts(guc) \
+	llist_del_all(&guc->submission_state.destroyed_contexts)
+
 static void guc_flush_destroyed_contexts(struct intel_guc *guc)
 {
-	struct intel_context *ce;
-	unsigned long flags;
+	struct intel_context *ce, *cn;
 
 	GEM_BUG_ON(!submission_disabled(guc) &&
 		   guc_submission_initialized(guc));
 
-	while (!list_empty(&guc->submission_state.destroyed_contexts)) {
-		spin_lock_irqsave(&guc->submission_state.lock, flags);
-		ce = list_first_entry_or_null(&guc->submission_state.destroyed_contexts,
-					      struct intel_context,
-					      destroyed_link);
-		if (ce)
-			list_del_init(&ce->destroyed_link);
-		spin_unlock_irqrestore(&guc->submission_state.lock, flags);
-
-		if (!ce)
-			break;
-
+	llist_for_each_entry_safe(ce, cn, take_destroyed_contexts(guc),
+				 destroyed_link) {
 		release_guc_id(guc, ce);
 		__guc_context_destroy(ce);
 	}
@@ -2723,23 +2715,11 @@ static void guc_flush_destroyed_contexts(struct intel_guc *guc)
 
 static void deregister_destroyed_contexts(struct intel_guc *guc)
 {
-	struct intel_context *ce;
-	unsigned long flags;
-
-	while (!list_empty(&guc->submission_state.destroyed_contexts)) {
-		spin_lock_irqsave(&guc->submission_state.lock, flags);
-		ce = list_first_entry_or_null(&guc->submission_state.destroyed_contexts,
-					      struct intel_context,
-					      destroyed_link);
-		if (ce)
-			list_del_init(&ce->destroyed_link);
-		spin_unlock_irqrestore(&guc->submission_state.lock, flags);
-
-		if (!ce)
-			break;
+	struct intel_context *ce, *cn;
 
+	llist_for_each_entry_safe(ce, cn, take_destroyed_contexts(guc),
+				 destroyed_link)
 		guc_lrc_desc_unpin(ce);
-	}
 }
 
 static void destroyed_worker_func(struct work_struct *w)
@@ -2771,8 +2751,8 @@ static void guc_context_destroy(struct kref *kref)
 	if (likely(!destroy)) {
 		if (!list_empty(&ce->guc_id.link))
 			list_del_init(&ce->guc_id.link);
-		list_add_tail(&ce->destroyed_link,
-			      &guc->submission_state.destroyed_contexts);
+		llist_add(&ce->destroyed_link,
+			  &guc->submission_state.destroyed_contexts);
 	} else {
 		__release_guc_id(guc, ce);
 	}
-- 
2.34.1