[PATCH 3.16 062/328] udlfb: set optimal write delay

Ben Hutchings
2018-12-09T22:13:28Z

From: Mikulas Patocka <mpatocka@redhat.com>

commit bb24153a3f13dd0dbc1f8055ad97fe346d598f66 upstream.

The default delay 5 jiffies is too much when the kernel is compiled with
HZ=100 - it results in jumpy cursor in Xwindow.

In order to find out the optimal delay, I benchmarked the driver on
1280x720x30fps video. I found out that with HZ=1000, 10ms is acceptable,
but with HZ=250 or HZ=300, we need 4ms, so that the video is played
without any frame skips.

This patch changes the delay to this value.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
include/video/udlfb.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/video/udlfb.h
+++ b/include/video/udlfb.h
@@ -88,7 +88,7 @@ struct dlfb_data {
#define MIN_RAW_PIX_BYTES 2
#define MIN_RAW_CMD_BYTES (RAW_HEADER_BYTES + MIN_RAW_PIX_BYTES)

-#define DL_DEFIO_WRITE_DELAY 5 /* fb_deferred_io.delay in jiffies */
+#define DL_DEFIO_WRITE_DELAY msecs_to_jiffies(HZ <= 300 ? 4 : 10) /* optimal value for 720p video */
#define DL_DEFIO_WRITE_DISABLE (HZ*60) /* "disable" with long delay */

/* remove these once align.h patch is taken into kernel */