[Qemu-devel] [PATCH 3/3] vnc: throttle screen updates.

[Gerd Hoffmann <kraxel@redhat.com>]

This patch makes the vnc server code skip screen refreshes in case
there is data in the output buffer.  This reduces the refresh rate to
throttle the bandwidth needed in case the network link is saturated.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 vnc.c |   11 ++++++++++-
 vnc.h |    1 +
 2 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/vnc.c b/vnc.c
index de9edea..6d93215 100644
--- a/vnc.c
+++ b/vnc.c
@@ -657,6 +657,7 @@ static void send_framebuffer_update(VncState *vs, int x, int y, int w, int h)
 
 static void vnc_copy(VncState *vs, int src_x, int src_y, int dst_x, int dst_y, int w, int h)
 {
+    vs->force_update = 1;
     vnc_update_client(vs);
 
     vnc_write_u8(vs, 0);  /* msg id */
@@ -710,6 +711,12 @@ static void vnc_update_client(void *opaque)
         int saved_offset;
         int has_dirty = 0;
 
+        if (vs->output.offset && !vs->audio_cap && !vs->force_update) {
+            /* kernel send buffers are full -> drop frames to throttle */
+            qemu_mod_timer(vs->timer, qemu_get_clock(rt_clock) + VNC_REFRESH_INTERVAL);
+            return;
+        }
+
         vga_hw_update();
 
         /*
@@ -745,7 +752,7 @@ static void vnc_update_client(void *opaque)
             server_row += ds_get_linesize(vs->ds);
         }
 
-        if (!has_dirty && !vs->audio_cap) {
+        if (!has_dirty && !vs->audio_cap && !vs->force_update) {
             qemu_mod_timer(vs->timer, qemu_get_clock(rt_clock) + VNC_REFRESH_INTERVAL);
             return;
         }
@@ -789,6 +796,7 @@ static void vnc_update_client(void *opaque)
         vs->output.buffer[saved_offset] = (n_rectangles >> 8) & 0xFF;
         vs->output.buffer[saved_offset + 1] = n_rectangles & 0xFF;
         vnc_flush(vs);
+        vs->force_update = 0;
 
     }
 
@@ -1407,6 +1415,7 @@ static void framebuffer_update_request(VncState *vs, int incremental,
 
     int i;
     vs->need_update = 1;
+    vs->force_update = 1;
     if (!incremental) {
         for (i = 0; i < h; i++) {
             vnc_set_bits(vs->guest.dirty[y_position + i],
diff --git a/vnc.h b/vnc.h
index ce9aa49..3ae95f3 100644
--- a/vnc.h
+++ b/vnc.h
@@ -121,6 +121,7 @@ struct VncState
 
     VncDisplay *vd;
     int need_update;
+    int force_update;
     uint32_t features;
     int absolute;
     int last_x;
-- 
1.6.1.3