Since its inception, a partial ack (where the right edge of continous
data moves forwards) would clear the RTO timer. Thus if some sack
retransmission other than the initial segment retransmitted is lost,
the session would then be at the mercy of some other - longer waiting -
timer to make forward progress. The very first retransmission is typically the
most prone to encounter a still filled up queue. But that retransmissions is
covered by the still running RTO timer from the in-sequence phase at that point.
It is counter-intuitive to disable the RTO timer completely, once the very
first of possibly many dozends of packets that need to be retransmitted, makes
it to the receiver. It is more logical to restart the RTO timer when some
additional in-sequence data is acked.
Short of lost retransmission detection, this will help with a more timely
loss recovery, when SACK retransmissions still encounter a congested