igt/gem_mmap_gtt: Ignore effects of CPU caches for comparing WB

When measuring WB performance we have the issue that it allows CPU
caching which is many times faster than main memory!

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

1 files changed, 10 insertions, 7 deletions

diff --git a/tests/gem_mmap_gtt.c b/tests/gem_mmap_gtt.c
index c8819ad2..ef41bcc0 100644
--- a/tests/gem_mmap_gtt.c
+++ b/tests/gem_mmap_gtt.c
@@ -256,17 +256,20 @@ test_wc(int fd)
 
 	gtt_writes = 0;
 	igt_until_timeout(1) {
-		memcpy(cpu, gtt, 4096);
+		memcpy(gtt, cpu, 4096);
 		gtt_writes++;
 	}
 	igt_debug("%lu GTT writes in 1s\n", gtt_writes);
 
-	cpu_writes = 0;
-	igt_until_timeout(1) {
-		memcpy(cpu, cpu, 4096);
-		cpu_writes++;
-	}
-	igt_debug("%lu CPU writes in 1s\n", cpu_writes);
+	if (igt_setup_clflush()) {
+		cpu_writes = 0;
+		igt_until_timeout(1) {
+			igt_clflush_range(cpu, 4096);
+			cpu_writes++;
+		}
+		igt_debug("%lu CPU writes in 1s\n", cpu_writes);
+	} else
+		cpu_writes = gtt_writes;
 
 	munmap(cpu, 4096);
 	munmap(gtt, 4096);