[PATCH 4/4] drm/amdgpu: Optimize mutex usage

[Alex Xie]

Use rw_semaphore instead of mutex for bo_lists.

In original function amdgpu_bo_list_get, the waiting
for result->lock can be quite long while mutex
bo_list_lock was holding. It can make other tasks
waiting for bo_list_lock for long period too.
Change bo_list_lock to rw_semaphore can avoid most of
such long waiting.

Secondly, this patch allows several tasks(readers of idr)
to proceed at the same time.

Signed-off-by: Alex Xie <AlexBin.Xie at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu.h         |  3 ++-
 drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c | 14 +++++++-------
 drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c     |  3 +--
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
index 063fc73..bfc40d7 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
@@ -35,6 +35,7 @@
 #include <linux/rbtree.h>
 #include <linux/hashtable.h>
 #include <linux/dma-fence.h>
+#include <linux/rwsem.h>
 
 #include <ttm/ttm_bo_api.h>
 #include <ttm/ttm_bo_driver.h>
@@ -859,7 +860,7 @@ void amdgpu_ctx_mgr_fini(struct amdgpu_ctx_mgr *mgr);
 struct amdgpu_fpriv {
 	struct amdgpu_vm	vm;
 	struct amdgpu_bo_va	*prt_va;
-	struct mutex		bo_list_lock;
+	struct rw_semaphore	bo_list_lock;
 	struct idr		bo_list_handles;
 	struct amdgpu_ctx_mgr	ctx_mgr;
 	u32			vram_lost_counter;
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
index 4363f28..bfe736e 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
@@ -45,10 +45,10 @@ static int amdgpu_bo_list_create(struct amdgpu_fpriv *fpriv,
 	if (!*result)
 		return -ENOMEM;
 
-	mutex_lock(&fpriv->bo_list_lock);
+	down_read(&fpriv->bo_list_lock);
 	r = idr_alloc(&fpriv->bo_list_handles, *result,
 		      1, 0, GFP_KERNEL);
-	mutex_unlock(&fpriv->bo_list_lock);
+	up_read(&fpriv->bo_list_lock);
 
 	if (r < 0) {
 		kfree(*result);
@@ -67,17 +67,17 @@ static void amdgpu_bo_list_destroy(struct amdgpu_fpriv *fpriv, int id)
 {
 	struct amdgpu_bo_list *list;
 
-	mutex_lock(&fpriv->bo_list_lock);
+	down_write(&fpriv->bo_list_lock);
 	list = idr_remove(&fpriv->bo_list_handles, id);
 	if (list) {
 		/* Another user may have a reference to this list still */
 		mutex_lock(&list->lock);
 		mutex_unlock(&list->lock);
-		mutex_unlock(&fpriv->bo_list_lock);
+		up_write(&fpriv->bo_list_lock);
 		amdgpu_bo_list_free(list);
 	}
 	else {
-		mutex_unlock(&fpriv->bo_list_lock);
+		up_write(&fpriv->bo_list_lock);
 	}
 }
 
@@ -173,11 +173,11 @@ amdgpu_bo_list_get(struct amdgpu_fpriv *fpriv, int id)
 {
 	struct amdgpu_bo_list *result;
 
-	mutex_lock(&fpriv->bo_list_lock);
+	down_read(&fpriv->bo_list_lock);
 	result = idr_find(&fpriv->bo_list_handles, id);
 	if (result)
 		mutex_lock(&result->lock);
-	mutex_unlock(&fpriv->bo_list_lock);
+	up_read(&fpriv->bo_list_lock);
 	return result;
 }
 
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
index f68ced6..c4cba81 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
@@ -841,7 +841,7 @@ int amdgpu_driver_open_kms(struct drm_device *dev, struct drm_file *file_priv)
 			goto out_suspend;
 	}
 
-	mutex_init(&fpriv->bo_list_lock);
+	init_rwsem(&fpriv->bo_list_lock);
 	idr_init(&fpriv->bo_list_handles);
 
 	amdgpu_ctx_mgr_init(&fpriv->ctx_mgr);
@@ -900,7 +900,6 @@ void amdgpu_driver_postclose_kms(struct drm_device *dev,
 		amdgpu_bo_list_free(list);
 
 	idr_destroy(&fpriv->bo_list_handles);
-	mutex_destroy(&fpriv->bo_list_lock);
 
 	kfree(fpriv);
 	file_priv->driver_priv = NULL;
-- 
2.7.4