From ce4e07f6a4d89b9ad660775cf404d2a94a79f091 Mon Sep 17 00:00:00 2001
From: Simone Bordet <simone.bordet@gmail.com>
Date: Fri, 13 Dec 2013 13:39:28 +0100
Subject: [PATCH] Added comments about optimizations that may be included as
 part of fixing 423974 - Optimize flow control.

---
 .../main/java/org/eclipse/jetty/spdy/Flusher.java  | 10 ++++++++++
 .../org/eclipse/jetty/spdy/StandardSession.java    | 14 ++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/jetty-spdy/spdy-core/src/main/java/org/eclipse/jetty/spdy/Flusher.java b/jetty-spdy/spdy-core/src/main/java/org/eclipse/jetty/spdy/Flusher.java
index d5838a95be4..0be5f941d12 100644
--- a/jetty-spdy/spdy-core/src/main/java/org/eclipse/jetty/spdy/Flusher.java
+++ b/jetty-spdy/spdy-core/src/main/java/org/eclipse/jetty/spdy/Flusher.java
@@ -203,6 +203,16 @@ public class Flusher
 
             if (controller != null)
                 controller.write(flusherCB, buffers);
+
+            // TODO: optimization
+            // If the callback completely immediately, it means that
+            // the connection is not congested, and therefore we can
+            // write more data without blocking.
+            // Therefore we should check this condition and increase
+            // the write window, which means to things: autotune the
+            // MAX_GATHER parameter, and/or autotune the buffer returned
+            // by FrameBytes.getByteBuffer() (see also comment there).
+
             return State.SCHEDULED;
         }
 
diff --git a/jetty-spdy/spdy-core/src/main/java/org/eclipse/jetty/spdy/StandardSession.java b/jetty-spdy/spdy-core/src/main/java/org/eclipse/jetty/spdy/StandardSession.java
index 4c249e6d54a..5e51cbe6735 100644
--- a/jetty-spdy/spdy-core/src/main/java/org/eclipse/jetty/spdy/StandardSession.java
+++ b/jetty-spdy/spdy-core/src/main/java/org/eclipse/jetty/spdy/StandardSession.java
@@ -1163,6 +1163,20 @@ public class StandardSession implements ISession, Parser.Listener, Dumpable
                 IStream stream = getStream();
                 int windowSize = stream.getWindowSize();
 
+                // TODO: optimization
+                // Right now, we use the windowSize to chunk big buffers.
+                // However, if the window size is large, we may congest the
+                // connection, or favor one stream that does a big download,
+                // starving the other streams.
+                // Also, SPDY DATA frames have a maximum of 16 MiB size, which
+                // is not enforced here.
+                // We should have a configurable "preferredDataFrameSize"
+                // (or even better autotuning) that will allow to send chunks
+                // that will not starve other streams and small enough to
+                // not congest the connection, while avoiding to send too many
+                // TCP packets.
+                // See also comment in class Flusher.
+
                 size = dataInfo.available();
                 if (size > windowSize)
                     size = windowSize;