On Thu, Oct 19, 2017 at 07:37:33AM +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 <[email protected]>
> Reviewed-by: Daniel Vetter <[email protected]>
Still sounds like a reasonable idea.
-Daniel
> ---
> drivers/gpu/drm/i915/i915_gem.c | 23 ++++++++++++++++++++---
> 1 file changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index d699ea3ab80b..026cb52ece0b 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1240,7 +1240,23 @@ 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)) {
> + /*
> + * Avoid waking the device up if we can fallback, as
> + * waking/resuming is very slow (worst-case 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 {
> + /* No backing pages, no fallback, we must force GGTT access */
> + intel_runtime_pm_get(i915);
> + }
> +
> vma = i915_gem_object_ggtt_pin(obj, NULL, 0, 0,
> PIN_MAPPABLE |
> PIN_NONFAULT |
> @@ -1257,7 +1273,7 @@ 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);
> }
>
> @@ -1320,8 +1336,9 @@ 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;
> }
> --
> 2.15.0.rc1
>
> _______________________________________________
> Intel-gfx mailing list
> [email protected]
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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