[igt-dev] [PATCH i-g-t] i915/api_intel_bb: Only assert objects are unmoved for full-ppgtt

[Chris Wilson]

If we let an object idle in a shared GTT, it may be evicted by the
kernel in favour of another client. Thus, we have to be very careful
when asserting that two different executions of the same object will
be at the same address. If there's an idle point between the two
asserts, it will only be guaranteed to hold for full-ppgtt.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2754
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
---
 tests/i915/api_intel_bb.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/tests/i915/api_intel_bb.c b/tests/i915/api_intel_bb.c
index 0cb3192cb..18814d14d 100644
--- a/tests/i915/api_intel_bb.c
+++ b/tests/i915/api_intel_bb.c
@@ -505,10 +505,21 @@ static void blit(struct buf_ops *bops,
 	intel_bb_exec(ibb, intel_bb_offset(ibb), flags, true);
 	check_buf(dst, COLOR_77);
 
-	poff2_src = intel_bb_get_object_offset(ibb, src->handle);
-	poff2_dst = intel_bb_get_object_offset(ibb, dst->handle);
-	igt_assert(poff_src == poff2_src);
-	igt_assert(poff_dst == poff2_dst);
+	/*
+	 * Since we let the objects idle, if the GTT is shared another client
+	 * is liable to reuse our offsets for themselves, causing us to have
+	 * to relocate. We don't expect this to happen as LRU eviction should
+	 * try to avoid reuse, but we use random eviction instead as it is
+	 * much quicker! Given that the kernel is *allowed* to relocate objects,
+	 * we cannot assert that the objects remain in the same location, unless
+	 * we are in full control of our own GTT.
+	 */
+	if (gem_uses_full_ppgtt(i915)) {
+		igt_assert_eq_u64(intel_bb_get_object_offset(ibb, src->handle),
+				  poff_src);
+		igt_assert_eq_u64(intel_bb_get_object_offset(ibb, dst->handle),
+				  poff_dst);
+	}
 
 	intel_buf_destroy(src);
 	intel_buf_destroy(dst);
-- 
2.29.2