Re: [PATCH] hashed device lookup (Does NOT meet Linus' sumission

From: Matti Aarnio (matti.aarnio@zmailer.org)
Date: Sun Jan 07 2001 - 10:33:06 EST


On Sun, Jan 07, 2001 at 01:42:50PM +0000, Alan Cox wrote:
> > + * NOTE: That is no longer true with the addition of VLAN tags. Not
> > + * sure which should go first, but I bet it won't make much
> > + * difference if we are running VLANs. The good news is that
>
> It makes a lot of difference tha the vlan goes 2nd. Most sane people wont
> have vlans active on a high load interface.

        VLAN tag header appears as Layer-3 protocol, which then
        causes loop into VLAN reception code and back to generic
        Layer-3 receiver.

        I just tried to pull data from another machine, which
        is on normal port thru VLAN trunking port to receiving
        machine, and got fast-ether at wire speed. (As near as
        ncftp's 11.11 MB/sec is wirespeed..)

> So fix the algorithm. You want the list sorted at this point, or to generate
> a bitmap of free/used entries and scan the list then scan the map
>
> Question: How do devices with hardware vlan support fit into your model ?

        Hardware VLAN support at several network cards is just
        to recognize VLAN tags, and then do the right thing
        ( = skip 4 bytes ) when doing TCP/UDP checksum.

> Alan

/Matti Aarnio
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