Proposed patch, convert IFQ_MAXLEN to kernel tunable...

[Bruce M. Simpson]

Hi,

I agree with the intent of the change that IPv4 and IPv6 input queues 
should have a tunable queue length. However, the change provided is 
going to make the definition of IFQ_MAXLEN global and dependent upon a 
variable.

gnn at freebsd.org wrote:
> Hi,
>
> 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.
>   

This isn't appropriate for many uses of ifq's which might be internal to 
a given driver or subsystem, and which may use IFQ_MAXLEN for 
convenience, as Ruslan has pointed out. I have code elsewhere which does 
this.

Can you please do this on a per-protocol stack basis? i.e. give IPv4 and 
IPv6 their own TUNABLE queue length.

thanks
BMS