Subject: Re: random ip_id must be configurable
To: Jun-ichiro itojun Hagino <>
From: Jonathan Stone <jonathan@DSG.Stanford.EDU>
List: tech-net
Date: 09/11/2003 18:23:55
In message <>Jun-ichiro itojun Hagino writes
>>  * There are environments where the computational cost does not justify
>>   deploying this fix.
>	have you measured it?  i mean, not on the userland but macro benchmark
>	like scp/ftp/whatever.  i there *any* noticeable difference?
>	(if you use vax/pdp, yeah, maybe...)

1. Itojun, you're asking  the wrong question.  You committed the change.
   You changed the status-quo-ante.  The onus is on you to measure
   the performance.  (This goes for seveal recent changes, too.)

2. In compute-intensive environments, any additional CPU load is a
   change for the worse. (See what Thor said about compute cluster interconnects).

3. This is NetBSD. Yes, we support vaxes. We support sun-3s. 

4. *BSD gets used in embedded environments which can also (given
   that gigabit ethernet has become a commodity) every cycle counts, where
   CPUs cannot keep up with the network.
   One example: Jason Thorpe recently optimized how we fill in the MAC
   address for IP over Ethernet, because it made a measurable (and to him or Wasabi,
   worthwhile) improvement for StrongArm over gig-e.

5. I have bencmarked similar prng code on Pentium IV. Turns out shifts are
   particularly slow on P4s, and for (smiilar but diffeerent) code: and yes,
   the overhead is measurable.