[Intel-gfx] [PATCH i-g-t] lib: Do two writes to /proc/sys/vm/drop_caches again

[Petri Latvala]

The drop_caches sysctl has a max value of 4, so writing 7 to it just
fails. Avoid the earlier two-writes problem by seeking to the
beginning between writes.

Signed-off-by: Petri Latvala <petri.latvala at intel.com>
---
 lib/intel_os.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/lib/intel_os.c b/lib/intel_os.c
index b9f970d..cb3b062 100644
--- a/lib/intel_os.c
+++ b/lib/intel_os.c
@@ -299,11 +299,16 @@ void intel_purge_vm_caches(void)
 	if (fd < 0)
 		return;
 
+	/* BIT(2): Be quiet. Cannot be combined with other operations,
+	 * the sysctl has a max value of 4.
+	 */
+	igt_ignore_warn(write(fd, "4\n", 2));
+	igt_assert(lseek(fd, 0, SEEK_SET) == 0);
+
 	/* BIT(0): Drop page cache
 	 * BIT(1): Drop slab cache
-	 * BIT(2): Be quiet in future
 	 */
-	igt_ignore_warn(write(fd, "7\n", 2));
+	igt_ignore_warn(write(fd, "3\n", 2));
 	close(fd);
 }
 
-- 
2.9.3