drm/ttm: Add a bo list reserve fastpath (v2)

Makes it possible to reserve a list of buffer objects with a single
spin lock / unlock if there is no contention.
Should improve cpu usage on SMP kernels.

v2: Initialize private list members on reserve and don't call
ttm_bo_list_ref_sub() with zero put_count.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

5 files changed, 186 insertions, 28 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 148a322d8f5d..a586378b1b2b 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -169,7 +169,7 @@ int ttm_bo_wait_unreserved(struct ttm_buffer_object *bo, bool interruptible)
 }
 EXPORT_SYMBOL(ttm_bo_wait_unreserved);
 
-static void ttm_bo_add_to_lru(struct ttm_buffer_object *bo)
+void ttm_bo_add_to_lru(struct ttm_buffer_object *bo)
 {
         struct ttm_bo_device *bdev = bo->bdev;
         struct ttm_mem_type_manager *man;
@@ -191,11 +191,7 @@ static void ttm_bo_add_to_lru(struct ttm_buffer_object *bo)
         }
 }
 
-/**
- * Call with the lru_lock held.
- */
-
-static int ttm_bo_del_from_lru(struct ttm_buffer_object *bo)
+int ttm_bo_del_from_lru(struct ttm_buffer_object *bo)
 {
         int put_count = 0;
 
@@ -267,6 +263,15 @@ static void ttm_bo_ref_bug(struct kref *list_kref)
         BUG();
 }
 
+void ttm_bo_list_ref_sub(struct ttm_buffer_object *bo, int count,
+                         bool never_free)
+{
+        while (count--)
+                kref_put(&bo->list_kref,
+                         (never_free || (count >= 0)) ? ttm_bo_ref_bug :
+                         ttm_bo_release_list);
+}
+
 int ttm_bo_reserve(struct ttm_buffer_object *bo,
                    bool interruptible,
                    bool no_wait, bool use_sequence, uint32_t sequence)
@@ -282,8 +287,7 @@ int ttm_bo_reserve(struct ttm_buffer_object *bo,
                 put_count = ttm_bo_del_from_lru(bo);
         spin_unlock(&glob->lru_lock);
 
-        while (put_count--)
-                kref_put(&bo->list_kref, ttm_bo_ref_bug);
+        ttm_bo_list_ref_sub(bo, put_count, true);
 
         return ret;
 }
@@ -496,8 +500,7 @@ static void ttm_bo_cleanup_refs_or_queue(struct ttm_buffer_object *bo)
                 spin_unlock(&glob->lru_lock);
                 ttm_bo_cleanup_memtype_use(bo);
 
-                while (put_count--)
-                        kref_put(&bo->list_kref, ttm_bo_ref_bug);
+                ttm_bo_list_ref_sub(bo, put_count, true);
 
                 return;
         } else {
@@ -580,8 +583,7 @@ retry:
         spin_unlock(&glob->lru_lock);
         ttm_bo_cleanup_memtype_use(bo);
 
-        while (put_count--)
-                kref_put(&bo->list_kref, ttm_bo_ref_bug);
+        ttm_bo_list_ref_sub(bo, put_count, true);
 
         return 0;
 }
@@ -802,8 +804,7 @@ retry:
 
         BUG_ON(ret != 0);
 
-        while (put_count--)
-                kref_put(&bo->list_kref, ttm_bo_ref_bug);
+        ttm_bo_list_ref_sub(bo, put_count, true);
 
         ret = ttm_bo_evict(bo, interruptible, no_wait_reserve, no_wait_gpu);
         ttm_bo_unreserve(bo);
@@ -1783,8 +1784,7 @@ static int ttm_bo_swapout(struct ttm_mem_shrink *shrink)
         put_count = ttm_bo_del_from_lru(bo);
         spin_unlock(&glob->lru_lock);
 
-        while (put_count--)
-                kref_put(&bo->list_kref, ttm_bo_ref_bug);
+        ttm_bo_list_ref_sub(bo, put_count, true);
 
         /**
          * Wait for GPU, then move to system cached.
diff --git a/drivers/gpu/drm/ttm/ttm_execbuf_util.c b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
index c285c2902d15..201a71d111ec 100644
--- a/drivers/gpu/drm/ttm/ttm_execbuf_util.c
+++ b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
@@ -32,6 +32,72 @@
 #include <linux/sched.h>
 #include <linux/module.h>
 
+static void ttm_eu_backoff_reservation_locked(struct list_head *list)
+{
+        struct ttm_validate_buffer *entry;
+
+        list_for_each_entry(entry, list, head) {
+                struct ttm_buffer_object *bo = entry->bo;
+                if (!entry->reserved)
+                        continue;
+
+                if (entry->removed) {
+                        ttm_bo_add_to_lru(bo);
+                        entry->removed = false;
+
+                }
+                entry->reserved = false;
+                atomic_set(&bo->reserved, 0);
+                wake_up_all(&bo->event_queue);
+        }
+}
+
+static void ttm_eu_del_from_lru_locked(struct list_head *list)
+{
+        struct ttm_validate_buffer *entry;
+
+        list_for_each_entry(entry, list, head) {
+                struct ttm_buffer_object *bo = entry->bo;
+                if (!entry->reserved)
+                        continue;
+
+                if (!entry->removed) {
+                        entry->put_count = ttm_bo_del_from_lru(bo);
+                        entry->removed = true;
+                }
+        }
+}
+
+static void ttm_eu_list_ref_sub(struct list_head *list)
+{
+        struct ttm_validate_buffer *entry;
+
+        list_for_each_entry(entry, list, head) {
+                struct ttm_buffer_object *bo = entry->bo;
+
+                if (entry->put_count) {
+                        ttm_bo_list_ref_sub(bo, entry->put_count, true);
+                        entry->put_count = 0;
+                }
+        }
+}
+
+static int ttm_eu_wait_unreserved_locked(struct list_head *list,
+                                         struct ttm_buffer_object *bo)
+{
+        struct ttm_bo_global *glob = bo->glob;
+        int ret;
+
+        ttm_eu_del_from_lru_locked(list);
+        spin_unlock(&glob->lru_lock);
+        ret = ttm_bo_wait_unreserved(bo, true);
+        spin_lock(&glob->lru_lock);
+        if (unlikely(ret != 0))
+                ttm_eu_backoff_reservation_locked(list);
+        return ret;
+}
+
+
 void ttm_eu_backoff_reservation(struct list_head *list)
 {
         struct ttm_validate_buffer *entry;
@@ -61,35 +127,71 @@ EXPORT_SYMBOL(ttm_eu_backoff_reservation);
 
 int ttm_eu_reserve_buffers(struct list_head *list, uint32_t val_seq)
 {
+        struct ttm_bo_global *glob;
         struct ttm_validate_buffer *entry;
         int ret;
 
+        if (list_empty(list))
+                return 0;
+
+        list_for_each_entry(entry, list, head) {
+                entry->reserved = false;
+                entry->put_count = 0;
+                entry->removed = false;
+        }
+
+        entry = list_first_entry(list, struct ttm_validate_buffer, head);
+        glob = entry->bo->glob;
+
 retry:
+        spin_lock(&glob->lru_lock);
         list_for_each_entry(entry, list, head) {
                 struct ttm_buffer_object *bo = entry->bo;
 
-                entry->reserved = false;
-                ret = ttm_bo_reserve(bo, true, false, true, val_seq);
-                if (ret != 0) {
-                        ttm_eu_backoff_reservation(list);
-                        if (ret == -EAGAIN) {
-                                ret = ttm_bo_wait_unreserved(bo, true);
-                                if (unlikely(ret != 0))
-                                        return ret;
-                                goto retry;
-                        } else
+retry_this_bo:
+                ret = ttm_bo_reserve_locked(bo, true, true, true, val_seq);
+                switch (ret) {
+                case 0:
+                        break;
+                case -EBUSY:
+                        ret = ttm_eu_wait_unreserved_locked(list, bo);
+                        if (unlikely(ret != 0)) {
+                                spin_unlock(&glob->lru_lock);
+                                ttm_eu_list_ref_sub(list);
+                                return ret;
+                        }
+                        goto retry_this_bo;
+                case -EAGAIN:
+                        ttm_eu_backoff_reservation_locked(list);
+                        spin_unlock(&glob->lru_lock);
+                        ttm_eu_list_ref_sub(list);
+                        ret = ttm_bo_wait_unreserved(bo, true);
+                        if (unlikely(ret != 0))
                                 return ret;
+                        goto retry;
+                default:
+                        ttm_eu_backoff_reservation_locked(list);
+                        spin_unlock(&glob->lru_lock);
+                        ttm_eu_list_ref_sub(list);
+                        return ret;
                 }
 
                 entry->reserved = true;
                 if (unlikely(atomic_read(&bo->cpu_writers) > 0)) {
-                        ttm_eu_backoff_reservation(list);
+                        ttm_eu_backoff_reservation_locked(list);
+                        spin_unlock(&glob->lru_lock);
+                        ttm_eu_list_ref_sub(list);
                         ret = ttm_bo_wait_cpu(bo, false);
                         if (ret)
                                 return ret;
                         goto retry;
                 }
         }
+
+        ttm_eu_del_from_lru_locked(list);
+        spin_unlock(&glob->lru_lock);
+        ttm_eu_list_ref_sub(list);
+
         return 0;
 }
 EXPORT_SYMBOL(ttm_eu_reserve_buffers);
diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
index beafc156a535..b0fc9c12554b 100644
--- a/include/drm/ttm/ttm_bo_api.h
+++ b/include/drm/ttm/ttm_bo_api.h
@@ -364,6 +364,44 @@ extern int ttm_bo_validate(struct ttm_buffer_object *bo,
  */
 extern void ttm_bo_unref(struct ttm_buffer_object **bo);
 
+
+/**
+ * ttm_bo_list_ref_sub
+ *
+ * @bo: The buffer object.
+ * @count: The number of references with which to decrease @bo::list_kref;
+ * @never_free: The refcount should not reach zero with this operation.
+ *
+ * Release @count lru list references to this buffer object.
+ */
+extern void ttm_bo_list_ref_sub(struct ttm_buffer_object *bo, int count,
+                                bool never_free);
+
+/**
+ * ttm_bo_add_to_lru
+ *
+ * @bo: The buffer object.
+ *
+ * Add this bo to the relevant mem type lru and, if it's backed by
+ * system pages (ttms) to the swap list.
+ * This function must be called with struct ttm_bo_global::lru_lock held, and
+ * is typically called immediately prior to unreserving a bo.
+ */
+extern void ttm_bo_add_to_lru(struct ttm_buffer_object *bo);
+
+/**
+ * ttm_bo_del_from_lru
+ *
+ * @bo: The buffer object.
+ *
+ * Remove this bo from all lru lists used to lookup and reserve an object.
+ * This function must be called with struct ttm_bo_global::lru_lock held,
+ * and is usually called just immediately after the bo has been reserved to
+ * avoid recursive reservation from lru lists.
+ */
+extern int ttm_bo_del_from_lru(struct ttm_buffer_object *bo);
+
+
 /**
  * ttm_bo_lock_delayed_workqueue
  *
diff --git a/include/drm/ttm/ttm_bo_driver.h b/include/drm/ttm/ttm_bo_driver.h
index 8e0c848326b6..95068e6024db 100644
--- a/include/drm/ttm/ttm_bo_driver.h
+++ b/include/drm/ttm/ttm_bo_driver.h
@@ -864,6 +864,20 @@ extern int ttm_bo_reserve(struct ttm_buffer_object *bo,
                           bool interruptible,
                           bool no_wait, bool use_sequence, uint32_t sequence);
 
+
+/**
+ * ttm_bo_reserve_locked:
+ *
+ * Similar to ttm_bo_reserve, but must be called with the glob::lru_lock
+ * spinlock held, and will not remove reserved buffers from the lru lists.
+ * The function may release the LRU spinlock if it needs to sleep.
+ */
+
+extern int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
+                                 bool interruptible,
+                                 bool no_wait, bool use_sequence,
+                                 uint32_t sequence);
+
 /**
  * ttm_bo_unreserve
  *
diff --git a/include/drm/ttm/ttm_execbuf_util.h b/include/drm/ttm/ttm_execbuf_util.h
index cd2c475da9ea..fd09b8438977 100644
--- a/include/drm/ttm/ttm_execbuf_util.h
+++ b/include/drm/ttm/ttm_execbuf_util.h
@@ -41,7 +41,9 @@
  * @bo:             refcounted buffer object pointer.
  * @new_sync_obj_arg: New sync_obj_arg for @bo, to be used once
  * adding a new sync object.
- * @reservied:      Indicates whether @bo has been reserved for validation.
+ * @reserved:       Indicates whether @bo has been reserved for validation.
+ * @removed:        Indicates whether @bo has been removed from lru lists.
+ * @put_count:      Number of outstanding references on bo::list_kref.
  */
 
 struct ttm_validate_buffer {
@@ -49,6 +51,8 @@ struct ttm_validate_buffer {
         struct ttm_buffer_object *bo;
         void *new_sync_obj_arg;
         bool reserved;
+        bool removed;
+        int put_count;
 };
 
 /**