ui/spice: Add an option to submit gl_draw requests at fixed rate

In the specific case where the display layer (virtio-gpu) is using
dmabuf, and if remote clients are enabled (-spice gl=on,port=xxxx),
it makes sense to limit the maximum (streaming) rate (refresh rate)
to a fixed value using the GUI refresh timer. Otherwise, the updates
or gl_draw requests would be sent as soon as the Guest submits a new
frame which is not optimal as it would lead to increased network
traffic and wastage of GPU cycles if the frames get dropped.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Marc-André Lureau <marcandre.lureau@redhat.com>
Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc: Frediano Ziglio <freddy77@gmail.com>
Cc: Dongwon Kim <dongwon.kim@intel.com>
Cc: Michael Scherle <michael.scherle@rz.uni-freiburg.de>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Message-Id: <20250617043546.1022779-5-vivek.kasireddy@intel.com>

1 files changed, 52 insertions, 10 deletions

diff --git a/ui/spice-display.c b/ui/spice-display.c
index 0fb72f6d6f..e409b6bdb2 100644
--- a/ui/spice-display.c
+++ b/ui/spice-display.c
@@ -32,6 +32,7 @@
 
 bool spice_opengl;
 bool spice_remote_client;
+int spice_max_refresh_rate;
 
 int qemu_spice_rect_is_empty(const QXLRect* r)
 {
@@ -844,12 +845,32 @@ static void qemu_spice_gl_block_timer(void *opaque)
     warn_report("spice: no gl-draw-done within one second");
 }
 
+static void spice_gl_draw(SimpleSpiceDisplay *ssd,
+                           uint32_t x, uint32_t y, uint32_t w, uint32_t h)
+{
+    uint64_t cookie;
+
+    cookie = (uintptr_t)qxl_cookie_new(QXL_COOKIE_TYPE_GL_DRAW_DONE, 0);
+    spice_qxl_gl_draw_async(&ssd->qxl, x, y, w, h, cookie);
+}
+
 static void spice_gl_refresh(DisplayChangeListener *dcl)
 {
     SimpleSpiceDisplay *ssd = container_of(dcl, SimpleSpiceDisplay, dcl);
-    uint64_t cookie;
 
-    if (!ssd->ds || qemu_console_is_gl_blocked(ssd->dcl.con)) {
+    if (!ssd->ds) {
+        return;
+    }
+
+    if (qemu_console_is_gl_blocked(ssd->dcl.con)) {
+        if (spice_remote_client && ssd->gl_updates && ssd->have_scanout) {
+            glFlush();
+            spice_gl_draw(ssd, 0, 0,
+                          surface_width(ssd->ds), surface_height(ssd->ds));
+            ssd->gl_updates = 0;
+            /* E.g, to achieve 60 FPS, update_interval needs to be ~16.66 ms */
+            dcl->update_interval = 1000 / spice_max_refresh_rate;
+        }
         return;
     }
 
@@ -857,11 +878,8 @@ static void spice_gl_refresh(DisplayChangeListener *dcl)
     if (ssd->gl_updates && ssd->have_surface) {
         qemu_spice_gl_block(ssd, true);
         glFlush();
-        cookie = (uintptr_t)qxl_cookie_new(QXL_COOKIE_TYPE_GL_DRAW_DONE, 0);
-        spice_qxl_gl_draw_async(&ssd->qxl, 0, 0,
-                                surface_width(ssd->ds),
-                                surface_height(ssd->ds),
-                                cookie);
+        spice_gl_draw(ssd, 0, 0,
+                      surface_width(ssd->ds), surface_height(ssd->ds));
         ssd->gl_updates = 0;
     }
 }
@@ -954,6 +972,20 @@ static void qemu_spice_gl_scanout_disable(DisplayChangeListener *dcl)
     SimpleSpiceDisplay *ssd = container_of(dcl, SimpleSpiceDisplay, dcl);
 
     trace_qemu_spice_gl_scanout_disable(ssd->qxl.id);
+
+    /*
+     * We need to check for the case of "lost" updates, where a gl_draw
+     * was not submitted because the timer did not get a chance to run.
+     * One case where this happens is when the Guest VM is getting
+     * rebooted. If the console is blocked in this situation, we need
+     * to unblock it. Otherwise, newer updates would not take effect.
+     */
+    if (qemu_console_is_gl_blocked(ssd->dcl.con)) {
+        if (spice_remote_client && ssd->gl_updates && ssd->have_scanout) {
+            ssd->gl_updates = 0;
+            qemu_spice_gl_block(ssd, false);
+        }
+    }
     spice_server_gl_scanout(&ssd->qxl, NULL, 0, 0, NULL, NULL, 0, DRM_FORMAT_INVALID,
                             DRM_FORMAT_MOD_INVALID, false);
     qemu_spice_gl_monitor_config(ssd, 0, 0, 0, 0);
@@ -1061,7 +1093,6 @@ static void qemu_spice_gl_update(DisplayChangeListener *dcl,
     EGLint fourcc = 0;
     bool render_cursor = false;
     bool y_0_top = false; /* FIXME */
-    uint64_t cookie;
     uint32_t width, height, texture;
 
     if (!ssd->have_scanout) {
@@ -1159,8 +1190,19 @@ static void qemu_spice_gl_update(DisplayChangeListener *dcl,
     trace_qemu_spice_gl_update(ssd->qxl.id, w, h, x, y);
     qemu_spice_gl_block(ssd, true);
     glFlush();
-    cookie = (uintptr_t)qxl_cookie_new(QXL_COOKIE_TYPE_GL_DRAW_DONE, 0);
-    spice_qxl_gl_draw_async(&ssd->qxl, x, y, w, h, cookie);
+
+    /*
+     * In the case of remote clients, the submission of gl_draw request is
+     * deferred here, so that it can be submitted later (to spice server)
+     * from spice_gl_refresh() timer callback. This is done to ensure that
+     * Guest updates are submitted at a steady rate (e.g. 60 FPS) instead
+     * of submitting them arbitrarily.
+     */
+    if (spice_remote_client) {
+        ssd->gl_updates++;
+    } else {
+        spice_gl_draw(ssd, x, y, w, h);
+    }
 }
 
 static const DisplayChangeListenerOps display_listener_gl_ops = {