[TUHS] 386BSD released
Theodore Y. Ts'o
tytso at mit.edu
Sat Jul 17 01:44:26 AEST 2021
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
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