[Spice-devel] [spice-gtk PATCH v6 2/2] channel-usbredir: drop isoc packets on low bandwidth

[Victor Toso]

When channel wants to send much more data then the wire can handle, the
queue grows fast. This patch does not limit the queue growth but
introduces an internal API to check if queue size is too big.

This internal API is used in usbredir_buffered_output_size_callback
which is called before any isoc pacaket is queued in usbredir. The
usbredir implements the logic to:
 - only drop isoc packets
 - while dropping packtes does still give us video frames from and above
   10fps streams

An easy way to test locally is sharing and webcam and with tc:
    tc qdisc add dev lo root netem delay 100ms
    tc qdisc change dev lo root netem delay 1000ms
    tc qdisc del dev lo root netem

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1264156
---
 src/channel-usbredir.c   |  9 +++++++++
 src/spice-channel-priv.h |  2 ++
 src/spice-channel.c      | 19 ++++++++++++++++++-
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/channel-usbredir.c b/src/channel-usbredir.c
index 89f5c9d..dbcf0af 100644
--- a/src/channel-usbredir.c
+++ b/src/channel-usbredir.c
@@ -91,6 +91,7 @@ static void usbredir_log(void *user_data, int level, const char *msg);
 static int usbredir_read_callback(void *user_data, uint8_t *data, int count);
 static int usbredir_write_callback(void *user_data, uint8_t *data, int count);
 static void usbredir_write_flush_callback(void *user_data);
+static uint64_t usbredir_buffered_output_size_callback(void *user_data);
 
 static void *usbredir_alloc_lock(void);
 static void usbredir_lock_lock(void *user_data);
@@ -224,6 +225,8 @@ void spice_usbredir_channel_set_context(SpiceUsbredirChannel *channel,
                                    usbredirhost_fl_write_cb_owns_buffer);
     if (!priv->host)
         g_error("Out of memory allocating usbredirhost");
+
+    usbredirhost_set_buffered_output_size_cb(priv->host, usbredir_buffered_output_size_callback);
 }
 
 static gboolean spice_usbredir_channel_open_device(
@@ -461,6 +464,12 @@ void spice_usbredir_channel_get_guest_filter(
 /* ------------------------------------------------------------------ */
 /* callbacks (any context)                                            */
 
+static uint64_t usbredir_buffered_output_size_callback(void *user_data)
+{
+    g_return_val_if_fail(SPICE_IS_USBREDIR_CHANNEL(user_data), 0);
+    return spice_channel_get_queue_size(SPICE_CHANNEL(user_data));
+}
+
 /* Note that this function must be re-entrant safe, as it can get called
    from both the main thread as well as from the usb event handling thread */
 static void usbredir_write_flush_callback(void *user_data)
diff --git a/src/spice-channel-priv.h b/src/spice-channel-priv.h
index 436a521..4b2d1e6 100644
--- a/src/spice-channel-priv.h
+++ b/src/spice-channel-priv.h
@@ -111,6 +111,7 @@ struct _SpiceChannelPrivate {
     gboolean                    xmit_queue_blocked;
     STATIC_MUTEX                xmit_queue_lock;
     guint                       xmit_queue_wakeup_id;
+    guint64                     xmit_queue_size;
 
     char                        name[16];
     enum spice_channel_state    state;
@@ -171,6 +172,7 @@ void spice_channel_wakeup(SpiceChannel *channel, gboolean cancel);
 
 SpiceSession* spice_channel_get_session(SpiceChannel *channel);
 enum spice_channel_state spice_channel_get_state(SpiceChannel *channel);
+guint64 spice_channel_get_queue_size (SpiceChannel *channel);
 
 /* coroutine context */
 typedef void (*handler_msg_in)(SpiceChannel *channel, SpiceMsgIn *msg, gpointer data);
diff --git a/src/spice-channel.c b/src/spice-channel.c
index 2ce52c7..8b6125f 100644
--- a/src/spice-channel.c
+++ b/src/spice-channel.c
@@ -697,10 +697,12 @@ void spice_msg_out_send(SpiceMsgOut *out)
 {
     SpiceChannelPrivate *c;
     gboolean was_empty;
+    guint32 size;
 
     g_return_if_fail(out != NULL);
     g_return_if_fail(out->channel != NULL);
     c = out->channel->priv;
+    size = spice_marshaller_get_total_size(out->marshaller);
 
     STATIC_MUTEX_LOCK(c->xmit_queue_lock);
     if (c->xmit_queue_blocked) {
@@ -710,6 +712,7 @@ void spice_msg_out_send(SpiceMsgOut *out)
 
     was_empty = g_queue_is_empty(&c->xmit_queue);
     g_queue_push_tail(&c->xmit_queue, out);
+    c->xmit_queue_size = (was_empty) ? size : c->xmit_queue_size + size;
 
     /* One wakeup is enough to empty the entire queue -> only do a wakeup
        if the queue was empty, and there isn't one pending already. */
@@ -2104,8 +2107,11 @@ static void spice_channel_iterate_write(SpiceChannel *channel)
         STATIC_MUTEX_LOCK(c->xmit_queue_lock);
         out = g_queue_pop_head(&c->xmit_queue);
         STATIC_MUTEX_UNLOCK(c->xmit_queue_lock);
-        if (out)
+        if (out) {
+            guint32 size = spice_marshaller_get_total_size(out->marshaller);
+            c->xmit_queue_size = (c->xmit_queue_size < size) ? 0 : c->xmit_queue_size - size;
             spice_channel_write_msg(channel, out);
+        }
     } while (out);
 
     spice_channel_flushed(channel, TRUE);
@@ -2814,6 +2820,17 @@ enum spice_channel_state spice_channel_get_state(SpiceChannel *channel)
 }
 
 G_GNUC_INTERNAL
+guint64 spice_channel_get_queue_size (SpiceChannel *channel)
+{
+    guint64 size;
+    SpiceChannelPrivate *c = channel->priv;
+    STATIC_MUTEX_LOCK(c->xmit_queue_lock);
+    size = c->xmit_queue_size;
+    STATIC_MUTEX_UNLOCK(c->xmit_queue_lock);
+    return size;
+}
+
+G_GNUC_INTERNAL
 void spice_channel_swap(SpiceChannel *channel, SpiceChannel *swap, gboolean swap_msgs)
 {
     SpiceChannelPrivate *c = channel->priv;
-- 
2.5.0