drm/i915: Wait on vma activity before taking the mutex

Optimistically wait for the prior vma activity before taking the mutex
to minimise the mutex hold time while unbinding. We will then verify the
vma is idle with a second wait under the mutex to ensure it is safe to
unbind.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200123224459.38128-2-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index 4999882fbceb5b05ea968f161c6d94255f628b5a..84e03da0d5f9703a9a156cef8f7a531f6820931c 100644 (file)
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -1279,16 +1279,21 @@ int i915_vma_unbind(struct i915_vma *vma)
                /* XXX not always required: nop_clear_range */
                wakeref = intel_runtime_pm_get(&vm->i915->runtime_pm);
 
+       /* Optimistic wait before taking the mutex */
+       err = i915_vma_sync(vma);
+       if (err)
+               goto out_rpm;
+
        err = mutex_lock_interruptible(&vm->mutex);
        if (err)
-               return err;
+               goto out_rpm;
 
        err = __i915_vma_unbind(vma);
        mutex_unlock(&vm->mutex);
 
+out_rpm:
        if (wakeref)
                intel_runtime_pm_put(&vm->i915->runtime_pm, wakeref);
-
        return err;
 }