On Thu, Sep 05, 2013 at 03:29:01PM +0100, Chris Wilson wrote:
> The busy-ioctl is frequently called as it is used by clients treating
> buffer objects like fences and polling for completion. These frequent
> calls are especially subject to contention with multiple clients leading
> to a lot of busy-waiting due to mutex_spin_on_owner()). We can, in most
> cases, report whether the bo is idle without touching struct_mutex, and
> only resort to hitting the lock if we need to queue flushes for the bo.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_gem.c | 27 +++++++++++++++++++++------
> 1 file changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 3b942ce..fed0b39 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -4068,18 +4068,34 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
> {
> struct drm_i915_gem_busy *args = data;
> struct drm_i915_gem_object *obj;
> + struct intel_ring_buffer *ring;
> int ret;
>
> - ret = i915_mutex_lock_interruptible(dev);
> - if (ret)
> - return ret;
> -
> obj = to_intel_bo(drm_gem_object_lookup(dev, file, args->handle));
> if (&obj->base == NULL) {
> ret = -ENOENT;
> - goto unlock;
> + goto out_unlocked;
> }
>
> + /* Do an optimistic check for activity - we don't care about userspace
> + * racing with itself, that is always problematic.
> + */
> + ring = obj->ring;
> + if (ring && obj->last_read_seqno == ring->outstanding_lazy_seqno)
> + goto lock_and_flush;
Feels a bit too tricky ... How useful is just an
if (ACCESS_ONCE(obj->active))
goto lock_and_flush;
Cheers, Daniel
> +
> + args->busy = ring ? intel_ring_flag(ring) << 16 | 1 : 0;
> + ret = 0;
> +
> +out_unlocked:
> + drm_gem_object_unreference_unlocked(&obj->base);
> + return ret;
> +
> +lock_and_flush:
> + ret = i915_mutex_lock_interruptible(dev);
> + if (ret)
> + goto out_unlocked;
> +
> /* Count all active objects as busy, even if they are currently not used
> * by the gpu. Users of this interface expect objects to eventually
> * become non-busy without any further actions, therefore emit any
> @@ -4094,7 +4110,6 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
> }
>
> drm_gem_object_unreference(&obj->base);
> -unlock:
> mutex_unlock(&dev->struct_mutex);
> return ret;
> }
> --
> 1.8.4.rc3
>
> _______________________________________________
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> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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