[PATCH] drm/ttm: remove fence_lock
Thomas Hellstrom
thomas at shipmail.org
Thu Oct 18 00:28:04 PDT 2012
Hi, Maarten,
As you know I have been having my doubts about this change.
To me it seems insane to be forced to read the fence pointer under a
reserved lock, simply because when you take the reserve lock, another
process may have it and there is a substantial chance that that process
will also be waiting for idle while holding the reserve lock.
In essence, to read the fence pointer, there is a large chance you will
be waiting for idle to be able to access it. That's why it's protected by
a separate spinlock in the first place.
So even if this change might not affect current driver much it's a change
to the TTM api that leads to an IMHO very poor design.
/Thomas
On 10/12/2012 05:23 PM, Maarten Lankhorst wrote:
> With the nouveau calls fixed there were only 2 places left that used
> fence_lock without a reservation, those are fixed in this patch:
>
> ttm_bo_cleanup_refs_or_queue is fixed by simply doing things the other
> way around.
>
> ttm_bo_cleanup_refs is fixed by taking a reservation first, then a pointer
> to the fence object and backs off from the reservation if waiting has to
> be performed.
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at canonical.com>
> ---
> This patch should be applied only after all the previous patches I sent are applied,
> since it depends on sync_obj_arg removal (kinda, probably fails to apply otherwise),
> uses ttm_bo_is_reserved, and depends on nouveau wait behavior being fixed.
>
> drivers/gpu/drm/nouveau/nouveau_bo.c | 4 -
> drivers/gpu/drm/nouveau/nouveau_gem.c | 15 +---
> drivers/gpu/drm/radeon/radeon_object.c | 2 -
> drivers/gpu/drm/ttm/ttm_bo.c | 124 ++++++++++++--------------------
> drivers/gpu/drm/ttm/ttm_bo_util.c | 3 -
> drivers/gpu/drm/ttm/ttm_bo_vm.c | 5 -
> drivers/gpu/drm/ttm/ttm_execbuf_util.c | 2 -
> drivers/gpu/drm/vmwgfx/vmwgfx_drv.c | 3 -
> include/drm/ttm/ttm_bo_api.h | 12 +--
> include/drm/ttm/ttm_bo_driver.h | 3 -
> 10 files changed, 52 insertions(+), 121 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
> index cee7448..9749c45 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> @@ -1449,10 +1449,8 @@ nouveau_bo_fence(struct nouveau_bo *nvbo, struct nouveau_fence *fence)
> if (likely(fence))
> nouveau_fence_ref(fence);
>
> - spin_lock(&nvbo->bo.bdev->fence_lock);
> old_fence = nvbo->bo.sync_obj;
> nvbo->bo.sync_obj = fence;
> - spin_unlock(&nvbo->bo.bdev->fence_lock);
>
> nouveau_fence_unref(&old_fence);
> }
> @@ -1552,9 +1550,7 @@ nouveau_bo_vma_del(struct nouveau_bo *nvbo, struct nouveau_vma *vma)
> if (vma->node) {
> if (nvbo->bo.mem.mem_type != TTM_PL_SYSTEM) {
> ttm_bo_reserve(&nvbo->bo, false, false, false, 0);
> - spin_lock(&nvbo->bo.bdev->fence_lock);
> ttm_bo_wait(&nvbo->bo, false, false, false);
> - spin_unlock(&nvbo->bo.bdev->fence_lock);
> ttm_bo_unreserve(&nvbo->bo);
> nouveau_vm_unmap(vma);
> }
> diff --git a/drivers/gpu/drm/nouveau/nouveau_gem.c b/drivers/gpu/drm/nouveau/nouveau_gem.c
> index 6d8391d..eaa700a 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_gem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
> @@ -391,18 +391,11 @@ retry:
> static int
> validate_sync(struct nouveau_channel *chan, struct nouveau_bo *nvbo)
> {
> - struct nouveau_fence *fence = NULL;
> + struct nouveau_fence *fence = nvbo->bo.sync_obj;
> int ret = 0;
>
> - spin_lock(&nvbo->bo.bdev->fence_lock);
> - if (nvbo->bo.sync_obj)
> - fence = nouveau_fence_ref(nvbo->bo.sync_obj);
> - spin_unlock(&nvbo->bo.bdev->fence_lock);
> -
> - if (fence) {
> + if (fence)
> ret = nouveau_fence_sync(fence, chan);
> - nouveau_fence_unref(&fence);
> - }
>
> return ret;
> }
> @@ -614,9 +607,7 @@ nouveau_gem_pushbuf_reloc_apply(struct drm_device *dev,
> data |= r->vor;
> }
>
> - spin_lock(&nvbo->bo.bdev->fence_lock);
> ret = ttm_bo_wait(&nvbo->bo, false, false, false);
> - spin_unlock(&nvbo->bo.bdev->fence_lock);
> if (ret) {
> NV_ERROR(drm, "reloc wait_idle failed: %d\n", ret);
> break;
> @@ -848,11 +839,9 @@ nouveau_gem_ioctl_cpu_prep(struct drm_device *dev, void *data,
>
> ret = ttm_bo_reserve(&nvbo->bo, true, false, false, 0);
> if (!ret) {
> - spin_lock(&nvbo->bo.bdev->fence_lock);
> ret = ttm_bo_wait(&nvbo->bo, true, true, true);
> if (!no_wait && ret)
> fence = nouveau_fence_ref(nvbo->bo.sync_obj);
> - spin_unlock(&nvbo->bo.bdev->fence_lock);
>
> ttm_bo_unreserve(&nvbo->bo);
> }
> diff --git a/drivers/gpu/drm/radeon/radeon_object.c b/drivers/gpu/drm/radeon/radeon_object.c
> index 808c444..df430e4 100644
> --- a/drivers/gpu/drm/radeon/radeon_object.c
> +++ b/drivers/gpu/drm/radeon/radeon_object.c
> @@ -613,12 +613,10 @@ int radeon_bo_wait(struct radeon_bo *bo, u32 *mem_type, bool no_wait)
> r = ttm_bo_reserve(&bo->tbo, true, no_wait, false, 0);
> if (unlikely(r != 0))
> return r;
> - spin_lock(&bo->tbo.bdev->fence_lock);
> if (mem_type)
> *mem_type = bo->tbo.mem.mem_type;
> if (bo->tbo.sync_obj)
> r = ttm_bo_wait(&bo->tbo, true, true, no_wait);
> - spin_unlock(&bo->tbo.bdev->fence_lock);
> ttm_bo_unreserve(&bo->tbo);
> return r;
> }
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index f6d7026..69fc29b 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -498,28 +498,23 @@ 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) {
> + 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);
> + 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);
>
> spin_unlock(&glob->lru_lock);
> @@ -528,18 +523,11 @@ 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);
> @@ -565,25 +553,15 @@ 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);
> -
> - if (unlikely(ret != 0))
> - return ret;
> -
> spin_lock(&glob->lru_lock);
>
> - if (unlikely(list_empty(&bo->ddestroy))) {
> - spin_unlock(&glob->lru_lock);
> - return 0;
> - }
> -
> ret = ttm_bo_reserve_locked(bo, interruptible,
> no_wait_reserve, false, 0);
>
> @@ -592,18 +570,37 @@ retry:
> return ret;
> }
>
> - /**
> - * 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.
> - */
> + 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_wait(bo, false, false, true);
> +
> + if (ret) {
> + if (no_wait_gpu) {
> + atomic_set(&bo->reserved, 0);
> + wake_up_all(&bo->event_queue);
> + spin_unlock(&glob->lru_lock);
> + return ret;
> + }
>
> - if (unlikely(bo->sync_obj)) {
> + /**
> + * 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.
> + */
> +
> + sync_obj = driver->sync_obj_ref(&bo->sync_obj);
> 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;
> }
>
> @@ -735,9 +732,7 @@ static int ttm_bo_evict(struct ttm_buffer_object *bo, bool interruptible,
> struct ttm_placement placement;
> int 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)) {
> if (ret != -ERESTARTSYS) {
> @@ -1054,7 +1049,6 @@ int ttm_bo_move_buffer(struct ttm_buffer_object *bo,
> {
> int ret = 0;
> struct ttm_mem_reg mem;
> - struct ttm_bo_device *bdev = bo->bdev;
>
> BUG_ON(!ttm_bo_is_reserved(bo));
>
> @@ -1063,9 +1057,7 @@ int ttm_bo_move_buffer(struct ttm_buffer_object *bo,
> * Have the driver move function wait for idle when necessary,
> * instead of doing it here.
> */
> - spin_lock(&bdev->fence_lock);
> ret = ttm_bo_wait(bo, false, interruptible, no_wait_gpu);
> - spin_unlock(&bdev->fence_lock);
> if (ret)
> return ret;
> mem.num_pages = bo->num_pages;
> @@ -1554,7 +1546,6 @@ int ttm_bo_device_init(struct ttm_bo_device *bdev,
> bdev->glob = glob;
> bdev->need_dma32 = need_dma32;
> bdev->val_seq = 0;
> - spin_lock_init(&bdev->fence_lock);
> mutex_lock(&glob->device_list_mutex);
> list_add_tail(&bdev->device_list, &glob->device_list);
> mutex_unlock(&glob->device_list_mutex);
> @@ -1690,52 +1681,33 @@ int ttm_bo_wait(struct ttm_buffer_object *bo,
> bool lazy, bool interruptible, bool no_wait)
> {
> struct ttm_bo_driver *driver = bo->bdev->driver;
> - struct ttm_bo_device *bdev = bo->bdev;
> - void *sync_obj;
> int ret = 0;
>
> + WARN_ON_ONCE(!ttm_bo_is_reserved(bo));
> +
> if (likely(bo->sync_obj == NULL))
> return 0;
>
> - while (bo->sync_obj) {
> -
> + if (bo->sync_obj) {
> if (driver->sync_obj_signaled(bo->sync_obj)) {
> void *tmp_obj = bo->sync_obj;
> bo->sync_obj = NULL;
> clear_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags);
> - spin_unlock(&bdev->fence_lock);
> driver->sync_obj_unref(&tmp_obj);
> - spin_lock(&bdev->fence_lock);
> - continue;
> + return 0;
> }
>
> if (no_wait)
> return -EBUSY;
>
> - sync_obj = driver->sync_obj_ref(bo->sync_obj);
> - spin_unlock(&bdev->fence_lock);
> - ret = driver->sync_obj_wait(sync_obj,
> + ret = driver->sync_obj_wait(bo->sync_obj,
> lazy, interruptible);
> if (unlikely(ret != 0)) {
> - driver->sync_obj_unref(&sync_obj);
> - spin_lock(&bdev->fence_lock);
> return ret;
> }
> - spin_lock(&bdev->fence_lock);
> - if (likely(bo->sync_obj == sync_obj)) {
> - void *tmp_obj = bo->sync_obj;
> - bo->sync_obj = NULL;
> - clear_bit(TTM_BO_PRIV_FLAG_MOVING,
> - &bo->priv_flags);
> - spin_unlock(&bdev->fence_lock);
> - driver->sync_obj_unref(&sync_obj);
> - driver->sync_obj_unref(&tmp_obj);
> - spin_lock(&bdev->fence_lock);
> - } else {
> - spin_unlock(&bdev->fence_lock);
> - driver->sync_obj_unref(&sync_obj);
> - spin_lock(&bdev->fence_lock);
> - }
> + driver->sync_obj_unref(&bo->sync_obj);
> + clear_bit(TTM_BO_PRIV_FLAG_MOVING,
> + &bo->priv_flags);
> }
> return 0;
> }
> @@ -1799,9 +1771,7 @@ static int ttm_bo_swapout(struct ttm_mem_shrink *shrink)
> * Wait for GPU, then move to system cached.
> */
>
> - spin_lock(&bo->bdev->fence_lock);
> ret = ttm_bo_wait(bo, false, false, false);
> - spin_unlock(&bo->bdev->fence_lock);
>
> if (unlikely(ret != 0))
> goto out;
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index d80d1e8..84d6e01 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -622,7 +622,6 @@ int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
> struct ttm_buffer_object *ghost_obj;
> void *tmp_obj = NULL;
>
> - spin_lock(&bdev->fence_lock);
> if (bo->sync_obj) {
> tmp_obj = bo->sync_obj;
> bo->sync_obj = NULL;
> @@ -630,7 +629,6 @@ int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
> bo->sync_obj = driver->sync_obj_ref(sync_obj);
> if (evict) {
> ret = ttm_bo_wait(bo, false, false, false);
> - spin_unlock(&bdev->fence_lock);
> if (tmp_obj)
> driver->sync_obj_unref(&tmp_obj);
> if (ret)
> @@ -653,7 +651,6 @@ int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
> */
>
> set_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags);
> - spin_unlock(&bdev->fence_lock);
> if (tmp_obj)
> driver->sync_obj_unref(&tmp_obj);
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index a877813..55718c2 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> @@ -122,17 +122,14 @@ static int ttm_bo_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> * move.
> */
>
> - spin_lock(&bdev->fence_lock);
> if (test_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags)) {
> ret = ttm_bo_wait(bo, false, true, false);
> - spin_unlock(&bdev->fence_lock);
> if (unlikely(ret != 0)) {
> retval = (ret != -ERESTARTSYS) ?
> VM_FAULT_SIGBUS : VM_FAULT_NOPAGE;
> goto out_unlock;
> }
> - } else
> - spin_unlock(&bdev->fence_lock);
> + }
>
> ret = ttm_mem_io_lock(man, true);
> if (unlikely(ret != 0)) {
> diff --git a/drivers/gpu/drm/ttm/ttm_execbuf_util.c b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
> index 721886e..51b5e97 100644
> --- a/drivers/gpu/drm/ttm/ttm_execbuf_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
> @@ -207,7 +207,6 @@ 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);
>
> list_for_each_entry(entry, list, head) {
> @@ -218,7 +217,6 @@ void ttm_eu_fence_buffer_objects(struct list_head *list, void *sync_obj)
> entry->reserved = false;
> }
> spin_unlock(&glob->lru_lock);
> - spin_unlock(&bdev->fence_lock);
>
> list_for_each_entry(entry, list, head) {
> if (entry->old_sync_obj)
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
> index ed3c1e7..e038c9a 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
> @@ -251,13 +251,10 @@ static void vmw_dummy_query_bo_prepare(struct vmw_private *dev_priv)
> volatile SVGA3dQueryResult *result;
> bool dummy;
> int ret;
> - struct ttm_bo_device *bdev = &dev_priv->bdev;
> struct ttm_buffer_object *bo = dev_priv->dummy_query_bo;
>
> ttm_bo_reserve(bo, false, false, false, 0);
> - spin_lock(&bdev->fence_lock);
> ret = ttm_bo_wait(bo, false, false, false);
> - spin_unlock(&bdev->fence_lock);
> if (unlikely(ret != 0))
> (void) vmw_fallback_wait(dev_priv, false, true, 0, false,
> 10*HZ);
> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
> index 816d9b1..6c69224 100644
> --- a/include/drm/ttm/ttm_bo_api.h
> +++ b/include/drm/ttm/ttm_bo_api.h
> @@ -222,6 +222,8 @@ struct ttm_buffer_object {
> struct file *persistent_swap_storage;
> struct ttm_tt *ttm;
> bool evicted;
> + void *sync_obj;
> + unsigned long priv_flags;
>
> /**
> * Members protected by the bdev::lru_lock.
> @@ -242,16 +244,6 @@ struct ttm_buffer_object {
> atomic_t reserved;
>
> /**
> - * Members protected by struct buffer_object_device::fence_lock
> - * In addition, setting sync_obj to anything else
> - * than NULL requires bo::reserved to be held. This allows for
> - * checking NULL while reserved but not holding the mentioned lock.
> - */
> -
> - void *sync_obj;
> - unsigned long priv_flags;
> -
> - /**
> * Members protected by the bdev::vm_lock
> */
>
> diff --git a/include/drm/ttm/ttm_bo_driver.h b/include/drm/ttm/ttm_bo_driver.h
> index 0c8c3b5..aac101b 100644
> --- a/include/drm/ttm/ttm_bo_driver.h
> +++ b/include/drm/ttm/ttm_bo_driver.h
> @@ -515,8 +515,6 @@ struct ttm_bo_global {
> *
> * @driver: Pointer to a struct ttm_bo_driver struct setup by the driver.
> * @man: An array of mem_type_managers.
> - * @fence_lock: Protects the synchronizing members on *all* bos belonging
> - * to this device.
> * @addr_space_mm: Range manager for the device address space.
> * lru_lock: Spinlock that protects the buffer+device lru lists and
> * ddestroy lists.
> @@ -539,7 +537,6 @@ struct ttm_bo_device {
> struct ttm_bo_driver *driver;
> rwlock_t vm_lock;
> struct ttm_mem_type_manager man[TTM_NUM_MEM_TYPES];
> - spinlock_t fence_lock;
> /*
> * Protected by the vm lock.
> */
>
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