From 3e77b161c238191ed1b0f2f54858f71be800ebd7 Mon Sep 17 00:00:00 2001
From: Arvid Norberg <arvid@libtorrent.org>
Date: Sat, 20 Mar 2010 02:46:33 +0000
Subject: [PATCH] made the send_buffer_watermark performance warning more
 meaningful

---
 ChangeLog               |  1 +
 src/peer_connection.cpp | 31 +++++++++++++++++++++++--------
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 78934159e..d65a50d73 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,4 @@
+	* made the send_buffer_watermark performance warning more meaningful
 	* supports complete_ago extension
 	* dropped zlib as a dependency and builds using puff.c instead
 	* made the default cache size depend on available physical RAM
diff --git a/src/peer_connection.cpp b/src/peer_connection.cpp
index 333d78d45..64c4e8537 100644
--- a/src/peer_connection.cpp
+++ b/src/peer_connection.cpp
@@ -3997,13 +3997,6 @@ namespace libtorrent
 		else if (buffer_size_watermark > m_ses.settings().send_buffer_watermark)
 		{
 			buffer_size_watermark = m_ses.settings().send_buffer_watermark;
-			// #error only trigger this if we actually run out of send buffer
-			// while we're waiting for the disk
-			if (t->alerts().should_post<performance_alert>())
-			{
-				t->alerts().post_alert(performance_alert(t->get_handle()
-					, performance_alert::send_buffer_watermark_too_low));
-			}
 		}
 
 		while (!m_requests.empty()
@@ -4246,11 +4239,11 @@ namespace libtorrent
 			return;
 		}
 
+		int quota_left = m_quota[upload_channel];
 		// send the actual buffer
 		if (!m_send_buffer.empty())
 		{
 			int amount_to_send = m_send_buffer.size();
-			int quota_left = m_quota[upload_channel];
 			if (amount_to_send > quota_left)
 				amount_to_send = quota_left;
 
@@ -4266,6 +4259,28 @@ namespace libtorrent
 
 			m_channel_state[upload_channel] = peer_info::bw_network;
 		}
+		else if (m_reading_bytes > 0
+			&& quota_left > 0
+			&& !m_connecting
+			&& !m_requests.empty()
+			&& m_reading_bytes > m_ses.settings().send_buffer_watermark - 0x4000)
+		{
+			// we're stalled on the disk. We want to write and we can write
+			// but our send buffer is empty, waiting to be refilled from the disk
+			// this either means the disk is slower than the network connection
+			// or that our send buffer watermark is too small, because we can
+			// send it all before the disk gets back to us. That's why we only
+			// trigger this if we've also filled the allowed send buffer. The
+			// first request would not fill it all the way up because of the
+			// upload rate being virtually 0. If m_requests is empty, it doesn't
+			// matter anyway, because we don't have any more requests from the
+			// peer to hang on to the disk
+			if (t->alerts().should_post<performance_alert>())
+			{
+				t->alerts().post_alert(performance_alert(t->get_handle()
+					, performance_alert::send_buffer_watermark_too_low));
+			}
+		}
 	}
 
 	void peer_connection::setup_receive()