libtorrent uses a low watermark for send buffers to determine when a new piece should +be requested from the disk I/O subsystem, to be appended to the send buffer. The low +watermark is determined based on the send rate of the socket. It needs to be large +enough to not draining the socket's send buffer before the disk operation completes.
+The watermark is bound to a max value, to avoid buffer sizes growing out of control. +The default max send buffer size might not be enough to sustain very high upload rates, +and you might have to increase it. It's specified in bytes in +session_settings::send_buffer_watermark. The high_performance_seed() preset +sets this value to 5 MB.
+First of all, in order to allow many connections, set the global connection limit