Re: gigabit switch that supports jumbo frames?

In article <mF3dh.3204$cW3.2660@xxxxxxxxxxxxxxxx>,
Rick Jones <rick.jones2@xxxxxx> wrote:

glen herrmannsfeldt <gah@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
It would seem that the NIC should be able to process one burst
similar to the processing of a jumbo frame, and with only a little
extra work, IP should be able to do the same thing. IP could, for
example, give a 9000 MTU to TCP, accept the data, and then frame
burst it out. (That is, if full duplex gigabit supports it, which I
don't know.)

IP Framentation bad, TSO good, JumboFrame better :)

And even better than that is an operating system that allows the network
controller (NIC) to move data directly to/from application virtual
memory space, without *any* OS intervention. Such a scheme makes the
frame length almost completely irrelevant; the only issue becomes the
per-frame overhead (e.g., preamble, FCS, etc.), which is fairly
inconsequential, as opposed to the processing overhead, which is what
everyone in this thread has been discussing. That is, with proper OS/NIC
interaction, performance is no longer a strong function of frame length.

We (at DEC) employed exactly this scheme over *25 years ago* in the VAX
CI port architecture, which was used to create VAXclusters of multiple
mainframes, using a high-speed network for the backbone interconnect. At
that time, the hardware was considered incredibly complex and
expensive--over $20K (1978 dollars) per port. Today, the entire scheme
could easily be implemented in inexpensive silicon; what's a few hundred
thousand gates nowadays?

What is needed is to have the OS allow the NIC access to the system page
table, so that it can do the virtual-to-physical memory mapping itself,
page swap into physical memory as needed, and perform all appropriate
data transfers without asking the OS for any additional processing or
resources. VAX/VMS allowed this, but I know of no OS today where this
idea is implemented, or even feasible. (Disclaimer: I'm a network
architect, not an OS guru. I welcome comment and correction from those
who know more than I do about this subject. I did not design the VAX CI
architecture (I did work on the backbone network design), although I
used it extensively.)


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