drm/i915: Remove (struct_mutex) locking for wait-ioctl (033d549b) · Commits · 戴 / test

With a bit of care (and leniency) we can iterate over the object and wait for previous rendering to complete with judicial use of atomic reference counting. The ABI requires us to ensure that an active object is eventually flushed (like the busy-ioctl) which is guaranteed by our management of requests (i.e. everything that is submitted to hardware is flushed in the same request). All we have to do is ensure that we can detect when the requests are complete for reporting when the object is idle (without triggering ETIME), locklessly - this is handled by i915_gem_active_wait_unlocked(). The impact of this is actually quite small - the return to userspace following the wait was already lockless and so we don't see much gain in latency improvement upon completing the wait. What we do achieve here is completing an already finished wait without hitting the struct_mutex, our hold is quite short and so we are typically just a victim of contention rather than a cause - but it is still one less contention point! v2: Break up a long line. Signed-off-by:

Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by:

Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1470388464-28458-12-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

+12 −31

Original line number	Diff line number	Diff line
		@@ -2622,47 +2622,28 @@ int
		i915_gem_wait_ioctl(struct drm_device dev, void data, struct drm_file *file)
		{
		struct drm_i915_gem_wait *args = data;
		struct intel_rps_client *rps = to_rps_client(file);
		struct drm_i915_gem_object *obj;
		struct drm_i915_gem_request *requests[I915_NUM_ENGINES];
		int i, n = 0;
		int ret;
		unsigned long active;
		int idx, ret = 0;

		if (args->flags != 0)
		return -EINVAL;

		ret = i915_mutex_lock_interruptible(dev);
		if (ret)
		return ret;

		obj = i915_gem_object_lookup(file, args->bo_handle);
		if (!obj) {
		mutex_unlock(&dev->struct_mutex);
		if (!obj)
		return -ENOENT;
		}

		if (!i915_gem_object_is_active(obj))
		goto out;

		for (i = 0; i < I915_NUM_ENGINES; i++) {
		struct drm_i915_gem_request *req;

		req = i915_gem_active_get(&obj->last_read[i],
		&obj->base.dev->struct_mutex);
		if (req)
		requests[n++] = req;
		active = __I915_BO_ACTIVE(obj);
		for_each_active(active, idx) {
		s64 *timeout = args->timeout_ns >= 0 ? &args->timeout_ns : NULL;
		ret = i915_gem_active_wait_unlocked(&obj->last_read[idx], true,
		timeout, rps);
		if (ret)
		break;
		}

		out:
		i915_gem_object_put(obj);
		mutex_unlock(&dev->struct_mutex);

		for (i = 0; i < n; i++) {
		if (ret == 0)
		ret = i915_wait_request(requests[i], true,
		args->timeout_ns > 0 ? &args->timeout_ns : NULL,
		to_rps_client(file));
		i915_gem_request_put(requests[i]);
		}
		i915_gem_object_put_unlocked(obj);
		return ret;
		}

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