drm/i915: Handle idling during i915_gem_evict_something busy loops

i915_gem_evict_something() is charged with finding a slot within the GTT
that we may reuse. Since our goal is not to stall, we first look for a
slot that only overlaps idle vma. To this end, on the first pass we move
any active vma to the end of the search list. However, we only stopped
moving active vma after we see the first active vma twice. If during the
search, that first active vma completed, we would not notice and keep on
extending the search list.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1746
Fixes: 2850748ef876 ("drm/i915: Pull i915_vma_pin under the vm->mutex")
Fixes: b1e3177bd1d8 ("drm/i915: Coordinate i915_active with its own mutex")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: <stable@vger.kernel.org> # v5.5+
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200509115217.26853-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_gem_evict.c b/drivers/gpu/drm/i915/i915_gem_evict.c
index 0ba7b1e881c0823d8d14feb161d91c80f9fc82b0..6501939929d5d737f181e8b6edc6a6945467b4f6 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_evict.c
+++ b/drivers/gpu/drm/i915/i915_gem_evict.c
@@ -128,6 +128,13 @@ search_again:
        active = NULL;
        INIT_LIST_HEAD(&eviction_list);
        list_for_each_entry_safe(vma, next, &vm->bound_list, vm_link) {
+               if (vma == active) { /* now seen this vma twice */
+                       if (flags & PIN_NONBLOCK)
+                               break;
+
+                       active = ERR_PTR(-EAGAIN);
+               }
+
                /*
                 * We keep this list in a rough least-recently scanned order
                 * of active elements (inactive elements are cheap to reap).
@@ -143,21 +150,12 @@ search_again:
                 * To notice when we complete one full cycle, we record the
                 * first active element seen, before moving it to the tail.
                 */
-               if (i915_vma_is_active(vma)) {
-                       if (vma == active) {
-                               if (flags & PIN_NONBLOCK)
-                                       break;
-
-                               active = ERR_PTR(-EAGAIN);
-                       }
-
-                       if (active != ERR_PTR(-EAGAIN)) {
-                               if (!active)
-                                       active = vma;
+               if (active != ERR_PTR(-EAGAIN) && i915_vma_is_active(vma)) {
+                       if (!active)
+                               active = vma;
 
-                               list_move_tail(&vma->vm_link, &vm->bound_list);
-                               continue;
-                       }
+                       list_move_tail(&vma->vm_link, &vm->bound_list);
+                       continue;
                }
 
                if (mark_free(&scan, vma, flags, &eviction_list))