NOW is defined as MACHP(0)-ticks, so this is a pretty course timer
that can't go backwards on intel processors. this limits the timer's
resolution to HZ,
which on 9atom is 1000, and 100 on pretty much anything else. further
limiting the
resolution is the tcp retransmit timers which
cpu% cat /net/tcp/3/local
127.0.0.1!57796
cpu% cat /net/tcp/3/remote
127.0.0.1!17034
cpu% cat /net/tcp/3/status
Established qin 0 qout 0 rq 0.0 srtt 80 mdev 40 sst 1048560 cwin
258192 swin 10485604 rwin 10485604 qscale 4 timer.start 10
timer.count 10 rerecv 0 katimer.start 2400
