igt/gem_exec_flush: Use a cacheline stride

Look at different cachelines on each pass, otherwise each group of 16
flush the same cachline.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 4 insertions, 1 deletions

diff --git a/tests/gem_exec_flush.c b/tests/gem_exec_flush.c
index 347a79fd..0aa84fe0 100644
--- a/tests/gem_exec_flush.c
+++ b/tests/gem_exec_flush.c
@@ -152,7 +152,10 @@ static void run(int fd, unsigned ring, int nchild, int timeout,
 
 		igt_timeout(timeout) {
 			bool xor = (cycles >> 10) & 1;
-			i = cycles++ % 1024;
+			int idx = cycles++ % 1024;
+
+			/* Inspect a different cacheline each iteration */
+			i = 16 * (idx % 64) + (idx / 64);
 
 			obj[1].relocs_ptr = (uintptr_t)&reloc0[i];
 			obj[2].relocs_ptr = (uintptr_t)&reloc1[i];