Re: [9fans] running plan9 : an ideal setup?

[erik quanstrom <quanstro@quanstro.net>]

On Fri Nov 21 12:31:13 EST 2014, bakul@bitblocks.com wrote:
> This paper is well worth reading:
> http://groups.csail.mit.edu/ana/Publications/PubPDFs/1988Analysis%20TCP%20Processing%20Overhead.pdf
>
> While the traditional BSD implementation uses mbufs that complicate things, actual tcp processing can be done quite cheaply.

- ignores tcp checksum -- it alone will take a couple cycles per byte.
- ignores locking
	and i believe they've used the BKL to avoid locking any data structures, otherwise
	how could they process ip in 61 instructions?  actually there's proof of this in the
	timer instruction count -- 17.  that's not enough to acquire a lock.
- asserts that 300 instructions of x86 code -> 400 instructions of risc code, conservatively
	absolutely not if one of them is rep; movb  (which they appear to use)

in short, i see signs that this paper is not realistic.

furthermore, this sunny picture assumes an environment where tcp isn't giving any
benefit.  if you're not retransmitting a bit, you're not getting anything out of tcp.
i think this was the original point.

- erik