Re: [TUHS] 386BSD released

["Theodore Y. Ts'o" <tytso@mit.edu>]

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