[PATCH 04/10] drm/ttm: change fence_lock to inner lock, v3
Thomas Hellstrom
thellstrom at vmware.com
Mon Nov 19 07:04:13 PST 2012
On 11/19/2012 03:17 PM, Thomas Hellstrom wrote:
> Hi,
>
> This patch looks mostly good, although I think ttm_bo_cleanup_refs
> becomes overly complicated:
> Could this do, or am I missing something?
>
Actually, my version is bad, because ttm_bo_wait() is called with the
lru lock held.
/Thomas
>
> static int ttm_bo_cleanup_refs(struct ttm_buffer_object *bo,
> bool interruptible,
> bool no_wait_reserve,
> bool no_wait_gpu)
> {
> struct ttm_bo_device *bdev = bo->bdev;
> struct ttm_bo_global *glob = bo->glob;
> int put_count;
> int ret = 0;
>
> /*
> * First, reserve while making sure we're still on the
> * ddestroy list.
> */
> retry_reserve:
> spin_lock(&glob->lru_lock);
>
> if (unlikely(list_empty(&bo->ddestroy))) {
> spin_unlock(&glob->lru_lock);
> return 0;
> }
>
> ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
>
> if (unlikely(ret == -EBUSY)) {
> spin_unlock(&glob->lru_lock);
> if (likely(!no_wait_reserve))
> ret = ttm_bo_wait_unreserved(bo, interruptible);
> if (unlikely(ret != 0))
> return ret;
>
> goto retry_reserve;
> }
>
> BUG_ON(ret != 0);
>
> spin_lock(&bdev->fence_lock);
> ret = ttm_bo_wait(bo, false, interruptible, no_wait_gpu);
> spin_unlock(&bdev->fence_lock);
>
> if (unlikely(ret != 0)) {
> atomic_set(&bo->reserved, 0);
> wake_up_all(&bo->event_queue);
> spin_unlock(&glob->lru_lock);
> return ret;
> }
>
> put_count = ttm_bo_del_from_lru(bo);
> list_del_init(&bo->ddestroy);
> ++put_count;
>
> spin_unlock(&glob->lru_lock);
> ttm_bo_cleanup_memtype_use(bo);
>
> atomic_set(&bo_reserved, 0);
> wake_up_all(&bo->event_queue);
> ttm_bo_list_ref_sub(bo, put_count, true);
>
> return 0;
> }
>
>
> On 11/12/2012 03:00 PM, Maarten Lankhorst wrote:
>> I changed the hierarchy to make fence_lock the most inner lock,
>> instead of outer lock. This will simplify things slightly, and
>> hopefully makes it easier to make fence_lock global at one point
>> should it be needed.
>>
>> To make things clearer, I change the order around in ttm_bo_cleanup_refs
>> and ttm_bo_cleanup_refs_or_queue.
>>
>> A reservation is taken first, then fence lock is taken and a wait is
>> attempted.
>>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at canonical.com>
>>
>> v2:
>> - fix conflict with upstream race fix, simplifies ttm_bo_cleanup_refs
>> v3:
>> - change removal of fence_lock to making it a inner lock instead
>> ---
>> drivers/gpu/drm/ttm/ttm_bo.c | 95
>> ++++++++++++++++------------------
>> drivers/gpu/drm/ttm/ttm_execbuf_util.c | 4 +-
>> 2 files changed, 48 insertions(+), 51 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
>> index a3383a7..70285ff 100644
>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
>> @@ -478,28 +478,26 @@ static void ttm_bo_cleanup_refs_or_queue(struct
>> ttm_buffer_object *bo)
>> {
>> struct ttm_bo_device *bdev = bo->bdev;
>> struct ttm_bo_global *glob = bo->glob;
>> - struct ttm_bo_driver *driver;
>> + struct ttm_bo_driver *driver = bdev->driver;
>> void *sync_obj = NULL;
>> int put_count;
>> int ret;
>> - spin_lock(&bdev->fence_lock);
>> - (void) ttm_bo_wait(bo, false, false, true);
>> - if (!bo->sync_obj) {
>> -
>> - spin_lock(&glob->lru_lock);
>> -
>> - /**
>> - * Lock inversion between bo:reserve and bdev::fence_lock here,
>> - * but that's OK, since we're only trylocking.
>> - */
>> -
>> - ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
>> + spin_lock(&glob->lru_lock);
>> + ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
>> + if (!ret) {
>> + spin_lock(&bdev->fence_lock);
>> + ret = ttm_bo_wait(bo, false, false, true);
>> - if (unlikely(ret == -EBUSY))
>> + if (unlikely(ret == -EBUSY)) {
>> + sync_obj = driver->sync_obj_ref(bo->sync_obj);
>> + spin_unlock(&bdev->fence_lock);
>> + atomic_set(&bo->reserved, 0);
>> + wake_up_all(&bo->event_queue);
>> goto queue;
>> -
>> + }
>> spin_unlock(&bdev->fence_lock);
>> +
>> put_count = ttm_bo_del_from_lru(bo);
>> atomic_set(&bo->reserved, 0);
>> @@ -509,18 +507,11 @@ static void ttm_bo_cleanup_refs_or_queue(struct
>> ttm_buffer_object *bo)
>> ttm_bo_list_ref_sub(bo, put_count, true);
>> return;
>> - } else {
>> - spin_lock(&glob->lru_lock);
>> }
>> queue:
>> - driver = bdev->driver;
>> - if (bo->sync_obj)
>> - sync_obj = driver->sync_obj_ref(bo->sync_obj);
>> -
>> kref_get(&bo->list_kref);
>> list_add_tail(&bo->ddestroy, &bdev->ddestroy);
>> spin_unlock(&glob->lru_lock);
>> - spin_unlock(&bdev->fence_lock);
>> if (sync_obj) {
>> driver->sync_obj_flush(sync_obj);
>> @@ -546,54 +537,60 @@ static int ttm_bo_cleanup_refs(struct
>> ttm_buffer_object *bo,
>> bool no_wait_gpu)
>> {
>> struct ttm_bo_device *bdev = bo->bdev;
>> + struct ttm_bo_driver *driver = bdev->driver;
>> struct ttm_bo_global *glob = bo->glob;
>> int put_count;
>> int ret = 0;
>> + void *sync_obj;
>> retry:
>> - spin_lock(&bdev->fence_lock);
>> - ret = ttm_bo_wait(bo, false, interruptible, no_wait_gpu);
>> - spin_unlock(&bdev->fence_lock);
>> + spin_lock(&glob->lru_lock);
>> - if (unlikely(ret != 0))
>> - return ret;
>> + ret = ttm_bo_reserve_locked(bo, interruptible,
>> + no_wait_reserve, false, 0);
>> -retry_reserve:
>> - spin_lock(&glob->lru_lock);
>> + if (unlikely(ret)) {
>> + spin_unlock(&glob->lru_lock);
>> + return ret;
>> + }
>> if (unlikely(list_empty(&bo->ddestroy))) {
>> + atomic_set(&bo->reserved, 0);
>> + wake_up_all(&bo->event_queue);
>> spin_unlock(&glob->lru_lock);
>> return 0;
>> }
>> - ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
>> -
>> - if (unlikely(ret == -EBUSY)) {
>> - spin_unlock(&glob->lru_lock);
>> - if (likely(!no_wait_reserve))
>> - ret = ttm_bo_wait_unreserved(bo, interruptible);
>> - if (unlikely(ret != 0))
>> + spin_lock(&bdev->fence_lock);
>> + ret = ttm_bo_wait(bo, false, false, true);
>> + if (ret) {
>> + if (no_wait_gpu) {
>> + spin_unlock(&bdev->fence_lock);
>> + atomic_set(&bo->reserved, 0);
>> + wake_up_all(&bo->event_queue);
>> + spin_unlock(&glob->lru_lock);
>> return ret;
>> + }
>> - goto retry_reserve;
>> - }
>> -
>> - BUG_ON(ret != 0);
>> -
>> - /**
>> - * We can re-check for sync object without taking
>> - * the bo::lock since setting the sync object requires
>> - * also bo::reserved. A busy object at this point may
>> - * be caused by another thread recently starting an accelerated
>> - * eviction.
>> - */
>> + /**
>> + * Take a reference to the fence and unreserve, if the wait
>> + * was succesful and no new sync_obj was attached,
>> + * ttm_bo_wait in retry will return ret = 0, and end the loop.
>> + */
>> - if (unlikely(bo->sync_obj)) {
>> + sync_obj = driver->sync_obj_ref(&bo->sync_obj);
>> + spin_unlock(&bdev->fence_lock);
>> atomic_set(&bo->reserved, 0);
>> wake_up_all(&bo->event_queue);
>> spin_unlock(&glob->lru_lock);
>> +
>> + ret = driver->sync_obj_wait(bo->sync_obj, false,
>> interruptible);
>> + driver->sync_obj_unref(&sync_obj);
>> + if (ret)
>> + return ret;
>> goto retry;
>> }
>> + spin_unlock(&bdev->fence_lock);
>> put_count = ttm_bo_del_from_lru(bo);
>> list_del_init(&bo->ddestroy);
>> diff --git a/drivers/gpu/drm/ttm/ttm_execbuf_util.c
>> b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
>> index 1986d00..cd9e452 100644
>> --- a/drivers/gpu/drm/ttm/ttm_execbuf_util.c
>> +++ b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
>> @@ -213,8 +213,8 @@ void ttm_eu_fence_buffer_objects(struct list_head
>> *list, void *sync_obj)
>> driver = bdev->driver;
>> glob = bo->glob;
>> - spin_lock(&bdev->fence_lock);
>> spin_lock(&glob->lru_lock);
>> + spin_lock(&bdev->fence_lock);
>> list_for_each_entry(entry, list, head) {
>> bo = entry->bo;
>> @@ -223,8 +223,8 @@ void ttm_eu_fence_buffer_objects(struct list_head
>> *list, void *sync_obj)
>> ttm_bo_unreserve_locked(bo);
>> entry->reserved = false;
>> }
>> - spin_unlock(&glob->lru_lock);
>> spin_unlock(&bdev->fence_lock);
>> + spin_unlock(&glob->lru_lock);
>> list_for_each_entry(entry, list, head) {
>> if (entry->old_sync_obj)
>
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