Re: [PATCH] drm/i915: Unbind objects in shrinker only if device is runtime active

Chris Wilson
2015-12-24T14:32:53Z

On Thu, Dec 24, 2015 at 07:54:09PM +0530, Goel, Akash wrote:
>
>
> On 12/24/2015 5:52 PM, Chris Wilson wrote:
> >On Thu, Dec 24, 2015 at 04:16:08PM +0530, Praveen Paneri wrote:
> >>When the system is running low on memory, gem shrinker is invoked.
> >>In this process objects will be unbounded from GTT and unbinding process
> >>will require access to GTT(GTTADR) and also to fence register potentially.
> >>That requires a resume of gfx device, if suspended, in the shrinker path.
> >>Considering the power leakage due to intermediate resume, perform unbinding
> >>operation only if device is already runtime active.
> >>
> >>Signed-off-by: Akash Goel <akash.goel@intel.com>
> >>Signed-off-by: Praveen Paneri <praveen.paneri@intel.com>
> >>Cc: Chris Wilson <chris@chris-wilson.co.uk>
> >
> >Lgtm, the only complication is that we over report the number of
> >shrinkable objects. But that isn't such a big issue with the current
> >incarnation of the shrinker.
> >
> >>---
> >> drivers/gpu/drm/i915/i915_gem_shrinker.c | 11 +++++++++++
> >> 1 file changed, 11 insertions(+)
> >>
> >>diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
> >>index f7df54a..89350f4 100644
> >>--- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
> >>+++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
> >>@@ -89,6 +89,15 @@ i915_gem_shrink(struct drm_i915_private *dev_priv,
> >> i915_gem_retire_requests(dev_priv->dev);
> >>
> >> /*
> >>+ * Unbinding of objects will require HW access. Lets not wake
> >>+ * up gfx device just for this. Do the unbinding only if gfx
> >>+ * device is already active.
> >>+ */
> >>+ if ((flags & I915_SHRINK_BOUND) &&
> >>+ !intel_runtime_pm_get_noidle(dev_priv))
> >
> >Please line up contnuation lines with the opening bracking, hint cino=:0,(0 for vim.
> >
> >With the whitespace fixed,
> >Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> >
> >/* Unbinding of objects will require HW access; let us not wake up
> > * the device just to recover a little memory. If absolutely necessary,
> > * we will force the wake during oom-notifier.
> > */
>
> Sorry not fully sure but do we need to cover
> i915_gem_retire_requests() also ?

No. That is covered by the dev_priv->mm.busy wakeref.

> Actually retire_requests could also lead to a potential unbinding,
> if the last reference of a context goes away in that.

Indeed, also last object unreference could trigger an unbinding, and
even last vma use. All covered by the dev_priv->mm.busy wakeref held
whilst there are any requests in flight.

> There is a runtime_pm_get protection in i915_gem_free_object, so
> should not be a problem for ringbuffer & context image objects and
> most probably the i915_gem_context_clean would get completed before
> the device again goes into runtime suspend state.

No the one in i915_gem_free_object is actually wrong (granularity), and
hopefully will be fixed in the near future.
-Chris

--
Chris Wilson, Intel Open Source Technology Centre