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Re: [PATCH v5] display/gtk: get proper refreshrate

From: Philippe Mathieu-Daudé
Subject: Re: [PATCH v5] display/gtk: get proper refreshrate
Date: Wed, 8 Jan 2020 15:54:40 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2

On 1/8/20 1:13 PM, address@hidden wrote:
From: Nikola Pavlica <address@hidden>

Because some VMs in QEMU can get GPU virtualization (using technologies
such as iGVT-g, as mentioned previously), they could produce a video
output that had a higher display refresh rate than of what the GTK
display was displaying. (fxp. Playing a video game inside of a Windows
VM at 60 Hz, while the output stood locked at 33 Hz because of defaults
set in include/ui/console.h)

Since QEMU does indeed have internal systems for determining frame
times as defined in ui/console.c.
The code checks for a variable called update_interval that it later
uses for time calculation. This variable, however, isn't defined
anywhere in ui/gtk.c and instead ui/console.c just sets it to

update_interval represents the number of milliseconds per display
refresh, and by doing some math we get that 1000/30 = 33.33... Hz

This creates the mentioned problem and what this patch does is that it
checks for the display refresh rate reported by GTK itself (we can take
this as a safe value) and just converts it back to a number of
milliseconds per display refresh.

Signed-off-by: Nikola Pavlica <address@hidden>

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

  include/ui/gtk.h |  2 ++
  ui/gtk.c         | 10 ++++++++++
  2 files changed, 12 insertions(+)

diff --git a/include/ui/gtk.h b/include/ui/gtk.h
index d9eedad976..d1b230848a 100644
--- a/include/ui/gtk.h
+++ b/include/ui/gtk.h
@@ -28,6 +28,8 @@
  #include "ui/egl-context.h"
+#define MILLISEC_PER_SEC 1000000
  typedef struct GtkDisplayState GtkDisplayState;
typedef struct VirtualGfxConsole {
diff --git a/ui/gtk.c b/ui/gtk.c
index 692ccc7bbb..eb0efc70ee 100644
--- a/ui/gtk.c
+++ b/ui/gtk.c
@@ -1966,6 +1966,10 @@ static GSList *gd_vc_gfx_init(GtkDisplayState *s, 
VirtualConsole *vc,
                                GSList *group, GtkWidget *view_menu)
      bool zoom_to_fit = false;
+    int refresh_rate_millihz;
+    GdkDisplay *dpy = gtk_widget_get_display(s->window);
+    GdkWindow *win = gtk_widget_get_window(s->window);
+    GdkMonitor *monitor = gdk_display_get_monitor_at_window(dpy, win);
vc->label = qemu_console_get_label(con);
      vc->s = s;
@@ -2026,6 +2030,12 @@ static GSList *gd_vc_gfx_init(GtkDisplayState *s, 
VirtualConsole *vc,
vc->gfx.kbd = qkbd_state_init(con);
      vc->gfx.dcl.con = con;
+    refresh_rate_millihz = gdk_monitor_get_refresh_rate(monitor);
+    if (refresh_rate_millihz) {
+        vc->gfx.dcl.update_interval = MILLISEC_PER_SEC / refresh_rate_millihz;
+    }

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