Re: RFC: Hashing by VIF addr for rx of data packets.

[Johannes Berg <johannes@sipsolutions.net>]

On Tue, 2013-04-02 at 16:45 -0700, Ben Greear wrote:
> I notice that the rx logic currently walks through all stations when a NIC receives
> a packet.
> 
> With the attached patch, total TCP download throughput goes from 70Mbps to 190Mbps on
> my test system (Atom 1.6Ghz) with 50 station VIFs receiving TCP data streams.
> 
> The basic idea is to hash on the VIF addr (ie, what you see in 'ifconfig wlan0' as MAC
> address), and then look up stations using the hdr->addr1 in the rx logic.
> 
> The attached patch probably breaks monitor interfaces and other VIFs other than AP and
> STA.  It also changes the behaviour of PROMISC, but I'm not sure that is bad (is
> the old behaviour needed for anything useful?)
> 
> I'm thinking to store a count of all VIF types on a radio, and make
> this hash code only be enabled when only STA and AP exist.  Maybe later optimize
> so we can quickly find monitor or other VIF types to handle them properly.
> 
> Comments and suggestions are welcome.

Hmmm. I'm not really convinced this will make sense upstream. I'm kinda
fine with the single-station cache, but maintaining a whole other hash
table seems too much overhead for every use case but yours.

> +		/* If we have only station and AP interfaces, then hash on
> +		 * the destination MAC (ie, local sdata MAC).  Could add other
> +		 * device types as well, perhaps.  This changes 'promisc' behaviour,
> +		 * but not sure that is a bad thing.
> +		 */
> +		if (!is_multicast_ether_addr(hdr->addr1)) {
> +			sta = sta_info_get_by_vif(local, hdr->addr1);

AFAICT, this is also wrong for TDLS and other cases where we might
receive a frame that's not from the AP, even if it's only by accident or
from an attacker.

johannes