merged RC_1_1 into master

include/libtorrent/disk_io_thread.hpp

@@ -289,6 +289,12 @@ namespace aux {
 		~disk_io_thread();
 #endif
 
+		enum
+		{
+			// every 4:th thread is a hash thread
+			hasher_thread_divisor = 4
+		};
+
 		void set_settings(settings_pack const* sett);
 
 		void abort(bool wait);

src/disk_io_thread.cpp

@@ -321,7 +321,7 @@ constexpr disk_job_flags_t disk_interface::cache_hit;
 
 		int const num_threads = m_settings.get_int(settings_pack::aio_threads);
 		// add one hasher thread for every three generic threads
-		int const num_hash_threads = num_threads / 4;
+		int const num_hash_threads = num_threads / hasher_thread_divisor;
 		m_generic_threads.set_max_threads(num_threads - num_hash_threads);
 		m_hash_threads.set_max_threads(num_hash_threads);
 	}

src/torrent.cpp

@@ -2291,8 +2291,11 @@ bool is_downloading_state(int const st)
 			/ m_torrent_file->piece_length();
 		// if we only keep a single read operation in-flight at a time, we suffer
 		// significant performance degradation. Always keep at least two jobs
-		// outstanding
-		if (num_outstanding < 2) num_outstanding = 2;
+		// outstanding per hasher thread
+		int const min_outstanding = 2
+			* std::max(1, settings().get_int(settings_pack::aio_threads)
+				/ disk_io_thread::hasher_thread_divisor);
+		if (num_outstanding < min_outstanding) num_outstanding = min_outstanding;
 
 		// we might already have some outstanding jobs, if we were paused and
 		// resumed quickly, before the outstanding jobs completed