On Fri 22-06-18 16:36:49, Chris Wilson wrote:
> Quoting Michal Hocko (2018-06-22 16:02:42)
> > Hi,
> > this is an RFC and not tested at all. I am not very familiar with the
> > mmu notifiers semantics very much so this is a crude attempt to achieve
> > what I need basically. It might be completely wrong but I would like
> > to discuss what would be a better way if that is the case.
> >
> > get_maintainers gave me quite large list of people to CC so I had to trim
> > it down. If you think I have forgot somebody, please let me know
>
> > diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c
> > b/drivers/gpu/drm/i915/i915_gem_userptr.c
> > index 854bd51b9478..5285df9331fa 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> > @@ -112,10 +112,11 @@ static void del_object(struct i915_mmu_object *mo)
> > mo->attached = false;
> > }
> >
> > -static void i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier
> > *_mn,
> > +static int i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier
> > *_mn,
> > struct mm_struct *mm,
> > unsigned long start,
> > - unsigned long end)
> > + unsigned long end,
> > + bool blockable)
> > {
> > struct i915_mmu_notifier *mn =
> > container_of(_mn, struct i915_mmu_notifier, mn);
> > @@ -124,7 +125,7 @@ static void
> > i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
> > LIST_HEAD(cancelled);
> >
> > if (RB_EMPTY_ROOT(&mn->objects.rb_root))
> > - return;
> > + return 0;
>
> The principle wait here is for the HW (even after fixing all the locks
> to be not so coarse, we still have to wait for the HW to finish its
> access).
Is this wait bound or it can take basically arbitrary amount of time?
> The first pass would be then to not do anything here if
> !blockable.
something like this? (incremental diff)
diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c
b/drivers/gpu/drm/i915/i915_gem_userptr.c
index 5285df9331fa..e9ed0d2cfabc 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -122,6 +122,7 @@ static int
i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
container_of(_mn, struct i915_mmu_notifier, mn);
struct i915_mmu_object *mo;
struct interval_tree_node *it;
+ int ret = 0;
LIST_HEAD(cancelled);
if (RB_EMPTY_ROOT(&mn->objects.rb_root))
@@ -133,6 +134,10 @@ static int
i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
spin_lock(&mn->lock);
it = interval_tree_iter_first(&mn->objects, start, end);
while (it) {
+ if (!blockable) {
+ ret = -EAGAIN;
+ goto out_unlock;
+ }
/* The mmu_object is released late when destroying the
* GEM object so it is entirely possible to gain a
* reference on an object in the process of being freed
@@ -154,8 +159,10 @@ static int
i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
spin_unlock(&mn->lock);
/* TODO: can we skip waiting here? */
- if (!list_empty(&cancelled) && blockable)
+ if (!list_empty(&cancelled))
flush_workqueue(mn->wq);
+
+ return ret;
}
static const struct mmu_notifier_ops i915_gem_userptr_notifier = {
--
Michal Hocko
SUSE Labs
