Proposed patch, convert IFQ_MAXLEN to kernel tunable...

[gnn at freebsd.org]

At Wed, 24 Sep 2008 12:53:31 -0700,
John-Mark Gurney wrote:
> 
> George V. Neville-Neil wrote this message on Tue, Sep 23, 2008 at 15:29 -0400:
> > It turns out that the last time anyone looked at this constant was
> > before 1994 and it's very likely time to turn it into a kernel
> > tunable.  On hosts that have a high rate of packet transmission
> > packets can be dropped at the interface queue because this value is
> > too small.  Rather than make a sweeping code change I propose the
> > following change to the macro and updating a couple of places in the
> > IP and IPv6 stacks that were using this macro to set their own global
> > variables.
> 
> The better solution is to resurrect rwatson's patch that eliminates the
> interface queue, and does direct dispatch to the ethernet driver..
> Usually the driver has a queue of 512 or more packets already, so putting
> them into a second queue doesn't provide much benefit besides increasing
> the amount of locking necessary to deliver packets...

Actually I am making this change because I found on 10G hardware the
queue is too small.  Also, there are many systems where you might want
to up this, usually ones that are highly biased towards transmit only,
like a multicast repeater of some sort.

Best,
George