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

[Gerd Hoffmann <kraxel@redhat.com>]

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  Hi,

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.

cheers,
  Gerd

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>From e1a20de776afe0d108fa94b2170f6d5690f9a24c Mon Sep 17 00:00:00 2001
From: Gerd Hoffmann <kraxel@redhat.com>
Date: Mon, 16 Mar 2009 21:37:48 +0100
Subject: [PATCH 3/3] vnc: throttle screen updates.

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 0daaeac..8c60547 100644
--- a/vnc.c
+++ b/vnc.c
@@ -649,6 +649,7 @@ 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 */
@@ -704,6 +705,12 @@ static void vnc_update_client(void *opaque)
 
         vga_hw_update();
 
+        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;
+        }
+
         /*
          * Walk through the guest dirty map.
          * Check and copy modified bits from guest to server surface.
@@ -737,7 +744,7 @@ 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;
         }
@@ -781,6 +788,7 @@ 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;
 
     }
 
@@ -1398,6 +1406,7 @@ 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 c00fb00..0a2c66c 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