Re: http://www.nfr.net/nfr/mail-archive/nfr-users/1999/Feb/0110.html

Greg Lindahl (lindahl@cs.virginia.edu)
Fri, 23 Apr 1999 14:24:23 -0400 (EDT)


> > The bsd machines were sniffing 45,000 packets per second. Linux -- in
> > the default configuration -- can't even receive 45,000 packets per
> > second, because of the default setting of
> > /proc/sys/net/core/netdev_max_backlog.
>
> I've benched a Linux box with the standard settings doing over 55,000 packets
> per second _routing_ not just receiving.

But you had a tail-wind. I take it that the bottom half can execute
more than 100x a second if the machine is otherwise idle. But if
anything comes along and uses a whole timeslice, the backlog queue
fills (default size 300) and you start dropping packets on the floor.
Yes? No?

And routing is fairly efficient; it's all in the kernel, at
least. Sniffing, on the other hand, consumes a fair bit of extra CPU
time getting the data up to the user process and consuming it.

> The fun with NFR isnt the device backlog, its that BSD has a hack built into
> it basically solely for sniffing tools to use, and Linux doesn't.

That may be the key to getting to *really* high packet rates. But Linux,
pin their test, slowed down as the packet rate increased. That's what
made me suspect the backlog. But it's just a guess.

-- g

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