vlan patch

[Yar Tikhiy]

On Thu, Oct 20, 2005 at 10:51:00AM +0200, Ragnar Lonn wrote:
> Gleb Smirnoff wrote:
> 
> >Although the memory overhead is not noticable on modern i386 and amd64
> >PCs I don't think that we should waste so much memory. We should keep
> >in mind the existence of embedded architectures with little memory.
> >
> >In most cases people use 10 - 30 VLANs. I suggest to use a hash, like it
> >is already done in ng_vlan(4). This hash makes every sixteenth VLAN to fall
> >into same slot. Since most people allocate VLAN ids contiguously the hash
> >distribution should be good.
> >
> >Moreover, I suggest Yar and Ruslan to work together and make the hash code
> >shared between vlan(4) and ng_vlan(4), not copy-and-pasted.
> 
> It looks as if ng_vlan implements a standard hash. Wouldn't a hashtree 
> be a good
> compromise between speed and memory usage?  Of course, a 16-slot hash is 
> a lot
> better than no hash at all :-)

The only problem with the hash currently used in ng_vlan is that
it is fixed-width.  I think it will be easy to teach it how to cope
with variable bit-width of hash using the same xor-folding technique.
I hope I'll have free time this week-end to test the performance
of the approaches discussed since implementing them is no problem
at all.

-- 
Yar