16 Jul
2021
16 Jul
'21
5:44 p.m.
On Fri, Jul 16, 2021 at 10:40:56AM -0400, Clem Cole wrote:
A huge difference, as Ted I'm sure knows, is that you tended to have many
more serial lines than network interfaces. I suspect Rob's scheme
would have sucked trying to support traditional single-byte serial
interfaces or really just use too much memory to be practical.
Network interfaces tend to be much faster than serial lines; at least
an order of magnitude. And with network interfaces you care about the
packet boundaries, and you want to process each packet separately. So
that makes things a lot harder than with serial interfaces.
With serial ports, 8k per serial port is plenty (2 x 2k flip buffers,
plus a 4k tty buffer between the mid-layer and userspace) for the
receive path. On the PDP-11, memory was much more constrained, so the
clist with each cblock storing 6 characters at a time in a linked list
was probably necessary. But even in the early days of the 386, you
could afford to make a different memory/performance tradeoff.
- Ted