> I've been wondering if it was possible to change the pty(4) internal > buffer size, as I noticed that ppp tunnels cannot use a larger frame > size. Because of this, it seems that the optimal MTU be 856, which is > so small that context switches become the bottleneck. > > It would be nice to for instance be able to use an MTU of 3000 so that > there are less context switches, but unfortunately tracing the > processes show that 1024 bytes are read from the pty devices at most. > > I looked at the various tty(4) termios(4) and pty(4) without finding an > option to change the buffer size. Is there a way at all to change it?
there's no option. infact, it's all hard coded as magic 1024 constants in about 4 places in sys/kern. i kept meaning to fix that, but haven't gotten around to it. i used to bump it to 10K avoid the xterm vs. size problem but that was fixed a while ago by christos, and i think that patch has been removed from my source trees. .mrg.