click perform effects with respect to RAM

[Eddie Kohler]

Hi Will,

> In reading the TOCS Click paper, the performance section doesn't mention
> the amount of memory used in the forwarding system.  

The TOCS paper does mention this about memory:

  1295 instructions are retired during the forwarding of a packet, implying
  that significantly more complex Click configurations could be supported
  without exhausting the Pentium III's 16K L1 instruction cache.

d-cache usage, of course, is mostly due to packets, and so shows up in the
forwarding rate graphs.

> Am I to interpret this as, the amount of memory does not significantly
> affect the perform within reason? Or should I assume that it can have
> affect, but to what extent it does is dependent largely on the
> configuration I'm using?

Amount of memory is important -- the performance limitation we see may be
due to memory system limits (depending on the machine). Your 2nd assumption
is a good one.

> We're pushing about 80,000 packets per second onto eth0.  The system we're
> thinking of running click on is a 1.4 Ghz P4 with 512 MB of RAM.  We don't
> have the memory at present, so I was curious about necessity of such an
> amount for this kind of use.

I think this system will be totally fine for your usage, as long as your
Ethernet cards are pollable (tulip-based 100MHz Ethernet, or Intel E1000
gig-E cards). You may squeak by even without polling.

Let us know if you have problems!

Eddie