On 07/10/2014 10:21 AM, Chris Wilson wrote:
Whilst I strongly advise against doing so for the implicit coherency
issues between the multiple buffer objects accessing the same backing
store, it nevertheless is a valid use case, akin to mmaping the same
file multiple times.
The reason why we forbade it earlier was that our use of the interval
tree for fast invalidation upon vma changes excluded overlapping
objects. So in the case where the user wishes to create such pairs of
overlapping objects, we degrade the range invalidation to walkin the
linear list of objects associated with the mm.
v2: Compile for mmu-notifiers after tweaking
[snip]
+static void invalidate_range__linear(struct i915_mmu_notifier *mn,
+ struct mm_struct *mm,
+ unsigned long start,
+ unsigned long end)
+{
+ struct i915_mmu_object *mmu;
+ unsigned long serial;
+
+restart:
+ serial = mn->serial;
+ list_for_each_entry(mmu, &mn->linear, link) {
+ struct drm_i915_gem_object *obj;
+
+ if (mmu->it.last < start || mmu->it.start > end)
+ continue;
+
+ obj = mmu->obj;
+ drm_gem_object_reference(&obj->base);
+ spin_unlock(&mn->lock);
+
+ cancel_userptr(obj);
+
+ spin_lock(&mn->lock);
+ if (serial != mn->serial)
+ goto restart;
+ }
+
+ spin_unlock(&mn->lock);
+}
+
static void i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier
*_mn,
struct mm_struct *mm,
unsigned long start,
@@ -60,16 +128,19 @@ static void
i915_gem_userptr_mn_invalidate_range_start(struct mmu_notifier *_mn,
{
struct i915_mmu_notifier *mn = container_of(_mn, struct
i915_mmu_notifier, mn);
struct interval_tree_node *it = NULL;
+ unsigned long next = start;
unsigned long serial = 0;
end--; /* interval ranges are inclusive, but invalidate range is
exclusive */
- while (start < end) {
+ while (next < end) {
struct drm_i915_gem_object *obj;
obj = NULL;
spin_lock(&mn->lock);
+ if (mn->is_linear)
+ return invalidate_range__linear(mn, mm, start, end);
Too bad that on first overlapping object the whole process goes into
"slow mode". I wonder what would benchmarking say to that.
Perhaps we could still use interval tree but add another layer of
indirection where ranges would be merged for overlapping objects and
contain a linear list of them only there?
Tvrtko
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