On Wed, Aug 30, 2017 at 06:48:19PM +0100, Chris Wilson wrote:
> If the device is in runtime suspend, resuming takes time and reduces our
> powersaving. If this was for a small write into an object, that resume
> will take longer than any savings in using the indirect GGTT access to
> avoid the cpu cache.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_gem.c | 21 ++++++++++++++++++---
> 1 file changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 93dfa793975a..8940a6873ca5 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1229,7 +1229,21 @@ i915_gem_gtt_pwrite_fast(struct drm_i915_gem_object *obj,
> if (ret)
> return ret;
>
> - intel_runtime_pm_get(i915);
> + if (i915_gem_object_has_struct_page(obj)) {
I don't really see why we need to check for has_struct_page here (we do
already outside the lock grabbing), and why if that's not the case we hit
the slow-path?
I'd have expected a simple s/pm_get/pm_get_if_in_use/ ...
-Daniel
> + /* Avoid waking the device up if we can fallback, as
> + * waking/resuming is very slow (10-100 ms depending
> + * on PCI sleeps and our own resume time). This easily
> + * dwarfs any performance advantage from using the
> + * cache bypass of indirect GGTT access.
> + */
> + if (!intel_runtime_pm_get_if_in_use(i915)) {
> + ret = -EFAULT;
> + goto out_unlock;
> + }
> + } else {
> + intel_runtime_pm_get(i915);
> + }
> +
> vma = i915_gem_object_ggtt_pin(obj, NULL, 0, 0,
> PIN_MAPPABLE | PIN_NONBLOCK);
> if (!IS_ERR(vma)) {
> @@ -1244,7 +1258,7 @@ i915_gem_gtt_pwrite_fast(struct drm_i915_gem_object *obj,
> if (IS_ERR(vma)) {
> ret = insert_mappable_node(ggtt, &node, PAGE_SIZE);
> if (ret)
> - goto out_unlock;
> + goto out_rpm;
> GEM_BUG_ON(!node.allocated);
> }
>
> @@ -1307,8 +1321,9 @@ i915_gem_gtt_pwrite_fast(struct drm_i915_gem_object *obj,
> } else {
> i915_vma_unpin(vma);
> }
> -out_unlock:
> +out_rpm:
> intel_runtime_pm_put(i915);
> +out_unlock:
> mutex_unlock(&i915->drm.struct_mutex);
> return ret;
> }
> --
> 2.14.1
>
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> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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