(TTMAXHIWAT + OBUFSIZ + 100) in case someone changes OBUFSIZ. 200
was to allow 100 above high water for ordinary writes and another
100 for kernel printfs.
Increased the reserved output queue count from 512 to the maximum
output queue count. This prevents exhaustion of clists and increases
the output throughput for 8 cy lines by almost a factor of 2 (on
a system where there aren't many other open ttys so clists become
exhausted after about 4 active lines (or earlier if TTMAXHIWAT is
increased :-]).
ttwrite() behaves very badly when clists are exhausted:
(1) it sleeps on lbolt instead of on TSA_OLOWAT(tp).
This could be fixed adequately by sleeping on TSA_OLOWAT(tp).
The nonzero reserved count guaratees that space will become
available independent of other ttys, and a reserved count
of 512 is barely enough for efficiency.
(2) it drops output if space runs out in the middle of special
output processing. This is too hard to fix without hardening
the reserved count. The watermark processing guarantees that
space doesn't run out only if the advertised space is guaranteed.
Increasing the reserved output queue count defeats the point of
dynamic allocation of clists. Previously, about 2K of memory per
tty was reserved (the raw queue was already reserved). Now, about
3.5K is reserved. Reserving everything would take a whole 0.5K
more.
247b53374b