releases/4.14.69/udlfb-set-optimal-write-delay.patch

   1 From bb24153a3f13dd0dbc1f8055ad97fe346d598f66 Mon Sep 17 00:00:00 2001
   2 From: Mikulas Patocka <mpatocka@redhat.com>
   3 Date: Wed, 25 Jul 2018 15:41:55 +0200
   4 Subject: udlfb: set optimal write delay
   5
   6 From: Mikulas Patocka <mpatocka@redhat.com>
   7
   8 commit bb24153a3f13dd0dbc1f8055ad97fe346d598f66 upstream.
   9
  10 The default delay 5 jiffies is too much when the kernel is compiled with
  11 HZ=100 - it results in jumpy cursor in Xwindow.
  12
  13 In order to find out the optimal delay, I benchmarked the driver on
  14 1280x720x30fps video. I found out that with HZ=1000, 10ms is acceptable,
  15 but with HZ=250 or HZ=300, we need 4ms, so that the video is played
  16 without any frame skips.
  17
  18 This patch changes the delay to this value.
  19
  20 Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
  21 Cc: stable@vger.kernel.org
  22 Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
  23 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  24
  25 ---
  26  include/video/udlfb.h |    2 +-
  27  1 file changed, 1 insertion(+), 1 deletion(-)
  28
  29 --- a/include/video/udlfb.h
  30 +++ b/include/video/udlfb.h
  31 @@ -88,7 +88,7 @@ struct dlfb_data {
  32  #define MIN_RAW_PIX_BYTES      2
  33  #define MIN_RAW_CMD_BYTES      (RAW_HEADER_BYTES + MIN_RAW_PIX_BYTES)
  34
  35 -#define DL_DEFIO_WRITE_DELAY    5 /* fb_deferred_io.delay in jiffies */
  36 +#define DL_DEFIO_WRITE_DELAY    msecs_to_jiffies(HZ <= 300 ? 4 : 10) /* optimal value for 720p video */
  37  #define DL_DEFIO_WRITE_DISABLE  (HZ*60) /* "disable" with long delay */
  38
  39  /* remove these once align.h patch is taken into kernel */