Re: [Qemu-devel] [PATCH] gtk: sync guest display updates to host display refresh

From: Chen Zhang <tgfbeta@me.com>
To: qemu-devel@nongnu.org
Cc: Gerd Hoffmann <kraxel@redhat.com>, tgfbeta@me.com
Subject: Re: [Qemu-devel] [PATCH] gtk: sync guest display updates to host display refresh
Date: Wed, 14 Nov 2018 11:10:57 +0800	[thread overview]
Message-ID: <0EE77C7B-02AF-4666-90D3-53BF09585EBD@me.com> (raw)
In-Reply-To: <20181113090249.15658-1-kraxel@redhat.com>

Hi,

I have briefly tested this patch. Unfortunately, it apparently caused deteriorated performance on a previously working Windows 10 guest with DMA Buf.

The patched qemu not only clogged up graphics drawing, but also obstructed the guest OS. The boot time and latency for guest operations (e.g. clicking Start menu in guest) dramatically increased. My best guess would be that GTK update events messed up with some polling in main_loop_wait(false), leading to blocked IO, or conversely the GUI being blocked by IO.

Best regards,

--
P.S:

The arguments for qemu:

/tmp/qemu-system-x86_64 -nodefaults -machine pc,accel=kvm,usb=off,kernel_irqchip=on \
  -vga none -display gtk,gl=on  -rtc base=localtime \
  -device vfio-pci,sysfsdev=/sys/bus/pci/devices/0000:00:02.0/{UUID-FOR-MDEV},x-igd-opregion=on,display=on,rombar=0 \
  -m 3000 -realtime mlock=off -smp 3,sockets=1,cores=1 \
  -drive file=/home/user/disk.img,format=qcow2,media=disk,if=ide \
  -usb -device qemu-xhci,id=xhci -device usb-tablet,bus=xhci.0 \
  -cpu host -monitor stdio

The host runs a Ubuntu 18.04 desktop.

> On Nov 13, 2018, at 5:02 PM, Gerd Hoffmann <kraxel@redhat.com> wrote:
> 
> Reduce console refresh timer to idle refresh rate.  Register a frame
> tick callback (called by gtk on each display frame) and use that to kick
> display updates instead.
> 
> That should sync qemu refresh rate to display refresh rate.  It'll also
> stop updating the qemu display in case the qemu is not visible (gtk
> stops calling the frame tick callback then).
> 
> Buglink: https://bugs.launchpad.net/bugs/1802915
> Suggested-by: Chen Zhang <tgfbeta@me.com>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
> ui/gtk.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
> 
> diff --git a/ui/gtk.c b/ui/gtk.c
> index 579990b865..8f79dfe42c 100644
> --- a/ui/gtk.c
> +++ b/ui/gtk.c
> @@ -1661,6 +1661,16 @@ static gboolean gd_configure(GtkWidget *widget,
>     return FALSE;
> }
> 
> +static gboolean gd_frame_tick(GtkWidget *widget,
> +                              GdkFrameClock *frame_clock,
> +                              gpointer opaque)
> +{
> +    VirtualConsole *vc = opaque;
> +
> +    vc->gfx.dcl.ops->dpy_refresh(&vc->gfx.dcl);
> +    return G_SOURCE_CONTINUE;
> +}
> +
> /** Virtual Console Callbacks **/
> 
> static GSList *gd_vc_menu_init(GtkDisplayState *s, VirtualConsole *vc,
> @@ -1911,6 +1921,12 @@ static void gd_connect_vc_gfx_signals(VirtualConsole *vc)
>                          G_CALLBACK(gd_focus_out_event), vc);
>         g_signal_connect(vc->gfx.drawing_area, "configure-event",
>                          G_CALLBACK(gd_configure), vc);
> +        if (1 /* make that a config option ??? */) {
> +            update_displaychangelistener(&vc->gfx.dcl,
> +                                         GUI_REFRESH_INTERVAL_IDLE);
> +            gtk_widget_add_tick_callback(vc->gfx.drawing_area,
> +                                         gd_frame_tick, vc, NULL);
> +        }
>     } else {
>         g_signal_connect(vc->gfx.drawing_area, "key-press-event",
>                          G_CALLBACK(gd_text_key_down), vc);
> -- 
> 2.9.3
> 