made seeding choking algorithm configurable

ChangeLog

@@ -1,3 +1,4 @@
+	* made seeding choking algorithm configurable
 	* deprecated setters for max connections, max half-open, upload and download
 	  rates and unchoke slots. These are now set through session_settings
 	* added functions to query an individual peer's upload and download limit

docs/manual.rst

@@ -3713,6 +3713,14 @@ session_settings
 
 		int choking_algorithm;
 		
+		enum seed_choking_algorithm_t
+		{
+			round_robin,
+			fastest_upload
+		};
+
+		int seed_choking_algorithm;
+
 		bool use_parole_mode;
 		int cache_size;
 		int cache_buffer_chunk_size;
@@ -4064,6 +4072,16 @@ The options for choking algorithms are:
 
 .. _paper: http://bittyrant.cs.washington.edu/#papers
 
+``seed_choking_algorithm`` controls the seeding unchoke behavior. The available
+options are:
+
+* ``round_robin`` which round-robins the peers that are unchoked when seeding. This
+  distributes the upload bandwidht uniformly and fairly. It minimizes the ability
+  for a peer to download everything without redistributing it.
+
+* ``fastest_upload`` unchokes the peers we can send to the fastest. This might be
+  a bit more reliable in utilizing all available capacity.
+
 ``use_parole_mode`` specifies if parole mode should be used. Parole mode means
 that peers that participate in pieces that fail the hash check are put in a mode
 where they are only allowed to download whole pieces. If the whole piece a peer

include/libtorrent/session_settings.hpp

@@ -136,6 +136,7 @@ namespace libtorrent
 			, auto_upload_slots_rate_based(true)
 #endif
 			, choking_algorithm(rate_based_choker)
+			, seed_choking_algorithm(round_robin)
 			, use_parole_mode(true)
 			, cache_size(1024)
 			, cache_buffer_chunk_size(16)
@@ -461,6 +462,15 @@ namespace libtorrent
 
 		int choking_algorithm;
 
+		enum seed_choking_algorithm_t
+		{
+			round_robin,
+			fastest_upload
+		};
+ 
+		// the choking algorithm to use for seeding torrents
+		int seed_choking_algorithm;
+		
 		// if set to true, peers that participate in a failing
 		// piece is put in parole mode. i.e. They will only
 		// download whole pieces until they either fail or pass.

src/peer_connection.cpp

@@ -398,6 +398,8 @@ namespace libtorrent
 		if (d1 > d2) return true;
 		if (d1 < d2) return false;
 
+		if (m_ses.settings().seed_choking_algorithm == session_settings::round_robin)
+		{
 			// in order to not switch back and forth too often,
 			// unchoked peers must be at least one piece ahead
 			// of a choked peer to be sorted at a lower unchoke-priority
@@ -407,6 +409,19 @@ namespace libtorrent
 
 			if (!c1_done && c2_done) return true;
 			if (c1_done && !c2_done) return false;
+		}
+		else if (m_ses.settings().seed_choking_algorithm == session_settings::fastest_upload)
+		{
+			size_type c1 = m_statistics.total_payload_upload() - m_uploaded_at_last_unchoke;
+			size_type c2 = rhs.m_statistics.total_payload_upload() - rhs.m_uploaded_at_last_unchoke;
+		
+			// take torrent priority into account
+			c1 *= 1 + t1->priority();
+			c2 *= 1 + t2->priority();
+
+			if (c1 > c2) return true;
+			if (c2 > c1) return false;
+		}
 		
 		// if both peers are still in their send quota or not in their send quota
 		// prioritize the one that has waited the longest to be unchoked
@@ -437,6 +452,8 @@ namespace libtorrent
 		if (c1 > c2) return true;
 		if (c1 < c2) return false;
 
+		if (m_ses.settings().seed_choking_algorithm == session_settings::round_robin)
+		{
 			// if they are equal, compare how much we have uploaded
 			c1 = m_statistics.total_payload_upload() - m_uploaded_at_last_unchoke;
 			c2 = rhs.m_statistics.total_payload_upload() - rhs.m_uploaded_at_last_unchoke;
@@ -450,7 +467,19 @@ namespace libtorrent
 
 			if (!c1_done && c2_done) return true;
 			if (c1_done && !c2_done) return false;
+		}	
+		else if (m_ses.settings().seed_choking_algorithm == session_settings::fastest_upload)
+		{
+			c1 = m_statistics.total_payload_upload() - m_uploaded_at_last_unchoke;
+			c2 = rhs.m_statistics.total_payload_upload() - rhs.m_uploaded_at_last_unchoke;
 		
+			// take torrent priority into account
+			c1 *= 1 + t1->priority();
+			c2 *= 1 + t2->priority();
+
+			if (c1 > c2) return true;
+			if (c2 > c1) return false;
+		}
 		// if both peers have are still in their send quota or not in their send quota
 		// prioritize the one that has waited the longest to be unchoked
 		return m_last_unchoke < rhs.m_last_unchoke;

src/session_impl.cpp

@@ -242,6 +242,7 @@ namespace aux {
 		TORRENT_SETTING(boolean, auto_upload_slots_rate_based)
 #endif
 		TORRENT_SETTING(integer, choking_algorithm)
+		TORRENT_SETTING(integer, seed_choking_algorithm)
 		TORRENT_SETTING(boolean, use_parole_mode)
 		TORRENT_SETTING(integer, cache_size)
 		TORRENT_SETTING(integer, cache_buffer_chunk_size)
@@ -2870,7 +2871,7 @@ namespace aux {
 
 			if (m_settings.choking_algorithm == session_settings::bittyrant_choker)
 			{
-				if (!p->is_choked())
+				if (!p->is_choked() && p->is_interesting())
 				{
 					policy::peer* pi = p->peer_info_struct();
 					if (!p->has_peer_choked())