On Sat, Nov 24, 2007 at 10:13:19PM +0100, Johannes Berg wrote: > > Eight bytes really sucks for wireless, many things are multiples of four > and QoS vs. non-QoS frames have a multiple of four and common hardware > only adds two padding bytes to get it aligned on four bytes so there's > no easy way to get hardware to align it properly. Hmm. Sorry I was wrong about the 8 bytes requirement. Although the IPv6 protocol does try to maintain an 8-byte alignment the Linux stack never does anything that requires that. So 4 bytes is enough. However, the wireless core is definitely not out of the woods. It needs to support variable hardware header lengths that are not always a multiple of 4. So here's my suggestion. Modify the wireless core to fix up any packets which aren't aligned correctly. That should make it work albeit in a way that's less than optimal. Then for each driver where you care about this performance (seriously I wouldn't for the speeds these things run at :), pick the most common wireless hardware header length and have the IP (or any other upper-level protocol) header aligned to at least 4 bytes. Or better if you know what hardware header length that you're going to get (e.g., based on what mode you're in) then do the skb_reserve accordingly. It's a good thing these things aren't running at 10Gb :) Cheers, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} <herbert@xxxxxxxxxxxxxxxxxxx> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt - To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
