Robert Pluim writes:

> Thatʼs always possible. You'd have to stick some instrumentation in
> things like connect_network_socket and wait_reading_process_output to
> narrow it down.
>
I think what happened is gnutls's internal buffering exhausts the
available data from the socket, so select blocks. There is an comment in
the code said gnutls leave one byte in the socket for select, but I
don't think it is doing this anymore. The following patch move the check
before the select and skip the select if there is data to be read in
gnutls. It fixed the occational stall in https.