diff options
| author | Chris Wilson <chris@chris-wilson.co.uk> | 2021-01-14 16:56:09 +0300 |
|---|---|---|
| committer | Chris Wilson <chris@chris-wilson.co.uk> | 2021-01-15 11:00:03 +0300 |
| commit | b2fe00bbb2b6bf06929dc300a4e3e91d9c12a3c9 (patch) | |
| tree | a4947eed4857aca73e654ce3097c5b38fb8b4849 /drivers | |
| parent | 163433e5c50afd8276f7dfdead4bf35f1bdafd05 (diff) | |
| download | linux-b2fe00bbb2b6bf06929dc300a4e3e91d9c12a3c9.tar.xz | |
drm/i915: Drop i915_request.lock serialisation around await_start
Originally, we used the signal->lock as a means of following the
previous link in its timeline and peeking at the previous fence.
However, we have replaced the explicit serialisation with a series of
very careful probes that anticipate the links being deleted and the
fences recycled before we are able to acquire a strong reference to it.
We do not need the signal->lock crutch anymore, nor want the contention.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210114135612.13210-2-chris@chris-wilson.co.uk
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/gpu/drm/i915/i915_request.c | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index 784c05ac5cca..973eceabbcca 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -969,9 +969,16 @@ i915_request_await_start(struct i915_request *rq, struct i915_request *signal) if (i915_request_started(signal)) return 0; + /* + * The caller holds a reference on @signal, but we do not serialise + * against it being retired and removed from the lists. + * + * We do not hold a reference to the request before @signal, and + * so must be very careful to ensure that it is not _recycled_ as + * we follow the link backwards. + */ fence = NULL; rcu_read_lock(); - spin_lock_irq(&signal->lock); do { struct list_head *pos = READ_ONCE(signal->link.prev); struct i915_request *prev; @@ -1002,7 +1009,6 @@ i915_request_await_start(struct i915_request *rq, struct i915_request *signal) fence = &prev->fence; } while (0); - spin_unlock_irq(&signal->lock); rcu_read_unlock(); if (!fence) return 0; |