From: Nikola Pavlica <pavlica.nikola@gmail.com>

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
GUI_REFRESH_INTERVAL_DEFAULT which is 30

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 <pavlica.nikola@gmail.com>
---
 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"
 #endif
 
+#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;
+    }
+
     register_displaychangelistener(&vc->gfx.dcl);
 
     gd_connect_vc_gfx_signals(vc);
-- 
2.24.1

On 1/8/20 1:13 PM, pavlica.nikola@gmail.com wrote:
> From: Nikola Pavlica <pavlica.nikola@gmail.com>
> 
> 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
> GUI_REFRESH_INTERVAL_DEFAULT which is 30
> 
> 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 <pavlica.nikola@gmail.com>

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

> ---
>   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"
>   #endif
>   
> +#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;
> +    }
> +
>       register_displaychangelistener(&vc->gfx.dcl);
>   
>       gd_connect_vc_gfx_signals(vc);
> 

On Wed, Jan 08, 2020 at 01:13:42PM +0100, pavlica.nikola@gmail.com wrote:
> From: Nikola Pavlica <pavlica.nikola@gmail.com>
> 
> 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
> GUI_REFRESH_INTERVAL_DEFAULT which is 30
> 
> 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 <pavlica.nikola@gmail.com>

Added to ui queue.

thanks,
  Gerd