[PATCH v3 2/2] drm/xe: Opportunistically skip TLB invalidaion on unbind

[Matthew Brost]

If a range or VMA is invalidated and scratch page is disabled, there
is no reason to issue a TLB invalidation on unbind, skip TLB
innvalidation is this condition is true. This is an opportunistic check
as it is done without the notifier lock, thus it possible for the range
to be invalidated after this check is performed.

This should improve performance of the SVM garbage collector, for
example, xe_exec_system_allocator --r many-stride-new-prefetch, went
~20s to ~9.5s on a BMG.

v2:
 - Use helper for valid check (Thomas)
v3:
 - Avoid skipping TLB invalidation if PTEs are removed at a higher
   level than the range
 - Never skip TLB invalidations for VMA
 - Drop Himal's RB

Signed-off-by: Matthew Brost <matthew.brost at intel.com>
---
 drivers/gpu/drm/xe/xe_pt.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
index 9c30111e8786..b6df8995e8c1 100644
--- a/drivers/gpu/drm/xe/xe_pt.c
+++ b/drivers/gpu/drm/xe/xe_pt.c
@@ -1995,6 +1995,32 @@ static int unbind_op_prepare(struct xe_tile *tile,
 	return 0;
 }
 
+static bool
+xe_pt_op_check_range_skip_invalidation(struct xe_vm_pgtable_update_op *pt_op,
+				       struct xe_svm_range *range)
+{
+	struct xe_vm_pgtable_update *update = pt_op->entries;
+
+	XE_WARN_ON(!pt_op->num_entries);
+
+	/*
+	 * We can't skip the invalidation if we are removing PTEs that span more
+	 * than the range, do some checks to ensure we are removing PTEs that
+	 * are invalid.
+	 */
+
+	if (pt_op->num_entries > 1)
+		return false;
+
+	if (update->pt->level == 0)
+		return true;
+
+	if (update->pt->level == 1)
+		return xe_svm_range_size(range) >= SZ_2M;
+
+	return false;
+}
+
 static int unbind_range_prepare(struct xe_vm *vm,
 				struct xe_tile *tile,
 				struct xe_vm_pgtable_update_ops *pt_update_ops,
@@ -2023,7 +2049,10 @@ static int unbind_range_prepare(struct xe_vm *vm,
 					 range->base.itree.last + 1);
 	++pt_update_ops->current_op;
 	pt_update_ops->needs_svm_lock = true;
-	pt_update_ops->needs_invalidation = true;
+	pt_update_ops->needs_invalidation |= xe_vm_has_scratch(vm) ||
+		xe_vm_has_valid_gpu_mapping(tile, range->tile_present,
+					    range->tile_invalidated) ||
+		!xe_pt_op_check_range_skip_invalidation(pt_op, range);
 
 	xe_pt_commit_prepare_unbind(XE_INVALID_VMA, pt_op->entries,
 				    pt_op->num_entries);
-- 
2.34.1