[Qemu-devel] [PATCH] sdl: Avoid unnecessary resizing of the display surface

[Qemu-devel] [PATCH] sdl: Avoid unnecessary resizing of the display surface

[Stefan Weil]

If neither width nor height changes, nothing has to be done.

Cc: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Stefan Weil <sw@weilnetz.de>
---

This patch improves SDL for any host (for example with remote X displays),
but the main reason why I wrote it was another problem:

On w32 / w64 hosts, qemu-system-arm has a deadlock when it calls
sdl_resize_displaysurface during Linux boot. One thread waits for
a critical region, another thread waits inside SDL_SetVideoMode.

The patch avoids this problem. Paolo, maybe you have an idea what
could cause the deadlock. Debugging on wxx is terrible - up to now,
I did not succeed in analysing the lock situation with gdb.

Regards,
Stefan W.

 ui/sdl.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/ui/sdl.c b/ui/sdl.c
index 8700b7a..8c1c71c 100644
--- a/ui/sdl.c
+++ b/ui/sdl.c
@@ -224,8 +224,11 @@ static void sdl_free_displaysurface(DisplaySurface *surface)
 
 static DisplaySurface* sdl_resize_displaysurface(DisplaySurface *surface, int width, int height)
 {
-    sdl_free_displaysurface(surface);
-    return sdl_create_displaysurface(width, height);
+    if (surface->width != width || surface->height != height) {
+        sdl_free_displaysurface(surface);
+        surface = sdl_create_displaysurface(width, height);
+    }
+    return surface;
 }
 
 /* generic keyboard conversion */
-- 
1.7.9

Re: [Qemu-devel] [PATCH] sdl: Avoid unnecessary resizing of the display surface

[Paolo Bonzini]

Il 01/05/2012 07:53, Stefan Weil ha scritto:
> If neither width nor height changes, nothing has to be done.
> 
> Cc: Anthony Liguori <aliguori@us.ibm.com>
> Signed-off-by: Stefan Weil <sw@weilnetz.de>
> ---
> 
> This patch improves SDL for any host (for example with remote X displays),
> but the main reason why I wrote it was another problem:
> 
> On w32 / w64 hosts, qemu-system-arm has a deadlock when it calls
> sdl_resize_displaysurface during Linux boot. One thread waits for
> a critical region, another thread waits inside SDL_SetVideoMode.
> 
> The patch avoids this problem. Paolo, maybe you have an idea what
> could cause the deadlock.

No idea---honestly, my w32 interest is limited to replacing hacks with
proper solutions. :)  It turns out that in many cases you can fix bugs
along the way and that helps having people look at your patches...

Paolo

Re: [Qemu-devel] [PATCH] sdl: Avoid unnecessary resizing of the display surface

[Stefan Weil]

Am 01.05.2012 07:53, schrieb Stefan Weil:
> If neither width nor height changes, nothing has to be done.
>
> Cc: Anthony Liguori<aliguori@us.ibm.com>
> Signed-off-by: Stefan Weil<sw@weilnetz.de>
> ---
>
> This patch improves SDL for any host (for example with remote X displays),
> but the main reason why I wrote it was another problem:
>
> On w32 / w64 hosts, qemu-system-arm has a deadlock when it calls
> sdl_resize_displaysurface during Linux boot. One thread waits for
> a critical region, another thread waits inside SDL_SetVideoMode.
>
> The patch avoids this problem. Paolo, maybe you have an idea what
> could cause the deadlock. Debugging on wxx is terrible - up to now,
> I did not succeed in analysing the lock situation with gdb.
>
> Regards,
> Stefan W.
>
>   ui/sdl.c |    7 +++++--
>   1 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/ui/sdl.c b/ui/sdl.c
> index 8700b7a..8c1c71c 100644
> --- a/ui/sdl.c
> +++ b/ui/sdl.c
> @@ -224,8 +224,11 @@ static void sdl_free_displaysurface(DisplaySurface *surface)
>
>   static DisplaySurface* sdl_resize_displaysurface(DisplaySurface *surface, int width, int height)
>   {
> -    sdl_free_displaysurface(surface);
> -    return sdl_create_displaysurface(width, height);
> +    if (surface->width != width || surface->height != height) {
> +        sdl_free_displaysurface(surface);
> +        surface = sdl_create_displaysurface(width, height);
> +    }
> +    return surface;
>   }
>
>   /* generic keyboard conversion */
>    

Please don't apply this patch. It is not complete and can cause a
crash (seen on w32 when resizing the SDL window).

I'll send an update.

Regards,
Stefan W.