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

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

[Gerd Hoffmann]

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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

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

[Stefano Stabellini]

Gerd Hoffmann wrote:

>   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.
> 




I like the idea behind this patch, but I would make force_update an
unsigned integer instead of a boolean, incrementing it every time we get a
framebuffer_update_request and decrementing it every time we send a
reply.

Secondly we could even move vga_hw_update after:

if (vs->output.offset && !vs->audio_cap && !vs->force_update)

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

[Gerd Hoffmann]

Stefano Stabellini wrote:
> I like the idea behind this patch, but I would make force_update an
> unsigned integer instead of a boolean, incrementing it every time we get a
> framebuffer_update_request and decrementing it every time we send a
> reply.

Point being?
Note that we can satisfy multiple update requests in one reply.
Also note that vnc_copy() sets force_update too.

> Secondly we could even move vga_hw_update after:
> 
> if (vs->output.offset && !vs->audio_cap && !vs->force_update)

Agreed.

cheers,
  Gerd

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

[Stefano Stabellini]

Gerd Hoffmann wrote:

> Point being?
> Note that we can satisfy multiple update requests in one reply.
> Also note that vnc_copy() sets force_update too.

right, not so useful then. I drop the suggestion.

[Qemu-devel] [PATCH 0/3] vnc patches

[Gerd Hoffmann]

  Hi,

Respin of the vnc patches.  Changes:

 * Rebased to latest svn (adapted to display allocator changes).
 * Moved vga_hw_update() in patch #3 as suggested by Stefano Stabellini.

cheers,
  Gerd

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

[Gerd Hoffmann]

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