Re: [PATCH] qemu/ui: set swap interval explicitly when OpenGL is enabled

[Marc-André Lureau]

On Wed, Sep 11, 2024 at 1:15 PM <gert.wollny@collabora.com> wrote:

From: Gert Wollny <gert.wollny@collabora.com>

Before 176e3783f2ab (ui/sdl2: OpenGL window context)
SDL_CreateRenderer was called unconditionally setting
the swap interval to 0. Since SDL_CreateRenderer is now no
longer called when OpenGL is enabled, the swap interval is
no longer set explicitly and vsync handling depends on
the environment settings which may lead to a performance
regression with virgl as reported in
   https://gitlab.com/qemu-project/qemu/-/issues/2565

Restore the old vsync handling by explicitly calling
SDL_GL_SetSwapInterval if OpenGL is enabled.

Fixes: 176e3783f2ab (ui/sdl2: OpenGL window context)
Closes: https://gitlab.com/qemu-project/qemu/-/issues/2565

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>

Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>

 

---
 ui/sdl2.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/ui/sdl2.c b/ui/sdl2.c
index 98ed974371..51299f3645 100644
--- a/ui/sdl2.c
+++ b/ui/sdl2.c
@@ -115,6 +115,7 @@ void sdl2_window_create(struct sdl2_console *scon)
         SDL_SetHint(SDL_HINT_RENDER_BATCHING, "1");

         scon->winctx = SDL_GL_CreateContext(scon->real_window);
+        SDL_GL_SetSwapInterval(0);
     } else {
         /* The SDL renderer is only used by sdl2-2D, when OpenGL is disabled */
         scon->real_renderer = SDL_CreateRenderer(scon->real_window, -1, 0);
--
2.44.2

--

Marc-André Lureau