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 From:  Fred Wright <fw at well dot com>
 To:  m0n0wall at lists dot m0n0 dot ch
 Subject:  Re: [m0n0wall] m0n0wall + net4501 keeps rebooting
 Date:  Tue, 30 Dec 2003 23:39:51 -0800 (PST)
On Wed, 31 Dec 2003, Manuel Kasper wrote:
> Fred Wright said:
> > I presume the HZ increase was only in that version, since the current
> > version seems to have 250.  Cranking it up to 1000 is actually a pretty
> > bad idea - see below.
> Yes, it was only for polling. From sys/i386/conf/LINT:
> ---
> # It is strongly recommended to use HZ=1000 or 2000 with DEVICE_POLLING
> # to achieve smoother behaviour.
> ---

2000?  Yikes!  Well, I suppose the clock service stays in the cache, with
only a few cycles of user code per tick to chase anything out. :-)

> > Only if wireless cards can generate sufficiently high packet rates to
> > cause trouble, which may well not be the case.
> Maybe not exactly "high packet rates", but apparently they can still
> generate enough CPU load, especially with WEP and/or IPsec...

Doing such complex processing at interrupt level isn't a very good idea,
but BSD (and Linux as well, I'll bet) doesn't make it easy to do it
efficiently any other way.

> > (well, OK, 500us average) is pretty significant.  What's really wanted is
> > a setup where packet processing is only delayed when the system is
> > "getting in trouble".  And of course at some point you have to start
> > throwing away packets when you can't keep up.
> Yep, but let's leave that to the FreeBSD developers, shall we? ;)

Sure.  Those were meant as general comments.