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dma-fence: Store the timestamp in the same union as the cb_list

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The timestamp and the cb_list are mutually exclusive, the cb_list can
only be added to prior to being signaled (and once signaled we drain),
while the timestamp is only valid upon being signaled. Both the
timestamp and the cb_list are only valid while the fence is alive, and
as soon as no references are held can be replaced by the rcu_head.

By reusing the union for the timestamp, we squeeze the base dma_fence
struct to 64 bytes on x86-64.

v2: Sort the union chronologically

Suggested-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Christian König <christian.koenig@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>.
Link: https://patchwork.freedesktop.org/patch/msgid/20190817153022.5749-1-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2019-08-17 16:30:22 +01:00
parent 0fc89b6802
commit f2cb60e9a3
4 changed files with 38 additions and 18 deletions
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16
drivers/dma-buf/dma-fence.c
View File

@ -129,6 +129,7 @@ EXPORT_SYMBOL(dma_fence_context_alloc);
int dma_fence_signal_locked(struct dma_fence *fence)
{
struct dma_fence_cb *cur, *tmp;
struct list_head cb_list;
lockdep_assert_held(fence->lock);
@ -136,16 +137,16 @@ int dma_fence_signal_locked(struct dma_fence *fence)
&fence->flags)))
return -EINVAL;
/* Stash the cb_list before replacing it with the timestamp */
list_replace(&fence->cb_list, &cb_list);
fence->timestamp = ktime_get();
set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
trace_dma_fence_signaled(fence);
if (!list_empty(&fence->cb_list)) {
list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
INIT_LIST_HEAD(&cur->node);
cur->func(fence, cur);
}
INIT_LIST_HEAD(&fence->cb_list);
list_for_each_entry_safe(cur, tmp, &cb_list, node) {
INIT_LIST_HEAD(&cur->node);
cur->func(fence, cur);
}
return 0;
@ -231,7 +232,8 @@ void dma_fence_release(struct kref *kref)
trace_dma_fence_destroy(fence);
if (WARN(!list_empty(&fence->cb_list),
if (WARN(!list_empty(&fence->cb_list) &&
!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags),
"Fence %s:%s:%llx:%llx released with pending signals!\n",
fence->ops->get_driver_name(fence),
fence->ops->get_timeline_name(fence),

13
drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
View File

@ -112,18 +112,18 @@ __dma_fence_signal__timestamp(struct dma_fence *fence, ktime_t timestamp)
}
static void
__dma_fence_signal__notify(struct dma_fence *fence)
__dma_fence_signal__notify(struct dma_fence *fence,
const struct list_head *list)
{
struct dma_fence_cb *cur, *tmp;
lockdep_assert_held(fence->lock);
lockdep_assert_irqs_disabled();
list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
list_for_each_entry_safe(cur, tmp, list, node) {
INIT_LIST_HEAD(&cur->node);
cur->func(fence, cur);
}
INIT_LIST_HEAD(&fence->cb_list);
}
void intel_engine_breadcrumbs_irq(struct intel_engine_cs *engine)
@ -185,11 +185,12 @@ void intel_engine_breadcrumbs_irq(struct intel_engine_cs *engine)
list_for_each_safe(pos, next, &signal) {
struct i915_request *rq =
list_entry(pos, typeof(*rq), signal_link);
__dma_fence_signal__timestamp(&rq->fence, timestamp);
struct list_head cb_list;
spin_lock(&rq->lock);
__dma_fence_signal__notify(&rq->fence);
list_replace(&rq->fence.cb_list, &cb_list);
__dma_fence_signal__timestamp(&rq->fence, timestamp);
__dma_fence_signal__notify(&rq->fence, &cb_list);
spin_unlock(&rq->lock);
i915_request_put(rq);

3
drivers/gpu/drm/vmwgfx/vmwgfx_fence.c
View File

@ -184,6 +184,9 @@ static long vmw_fence_wait(struct dma_fence *f, bool intr, signed long timeout)
spin_lock(f->lock);
if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &f->flags))
goto out;
if (intr && signal_pending(current)) {
ret = -ERESTARTSYS;
goto out;

24
include/linux/dma-fence.h
View File

@ -65,17 +65,31 @@ struct dma_fence_cb;
struct dma_fence {
spinlock_t *lock;
const struct dma_fence_ops *ops;
/* We clear the callback list on kref_put so that by the time we
* release the fence it is unused. No one should be adding to the cb_list
* that they don't themselves hold a reference for.
/*
* We clear the callback list on kref_put so that by the time we
* release the fence it is unused. No one should be adding to the
* cb_list that they don't themselves hold a reference for.
*
* The lifetime of the timestamp is similarly tied to both the
* rcu freelist and the cb_list. The timestamp is only set upon
* signaling while simultaneously notifying the cb_list. Ergo, we
* only use either the cb_list of timestamp. Upon destruction,
* neither are accessible, and so we can use the rcu. This means
* that the cb_list is *only* valid until the signal bit is set,
* and to read either you *must* hold a reference to the fence,
* and not just the rcu_read_lock.
*
* Listed in chronological order.
*/
union {
struct rcu_head rcu;
struct list_head cb_list;
/* @cb_list replaced by @timestamp on dma_fence_signal() */
ktime_t timestamp;
/* @timestamp replaced by @rcu on dma_fence_release() */
struct rcu_head rcu;
};
u64 context;
u64 seqno;
ktime_t timestamp;
unsigned long flags;
struct kref refcount;
int error;