Re: Optimizing performance for lots of virtual stations.

[Ben Greear <greearb@candelatech.com>]

On 03/14/2013 04:12 PM, Felix Fietkau wrote:
> On 2013-03-14 6:22 PM, Ben Greear wrote:
>> I've been doing some performance testing, and having lots of
>> stations causes quite a drag:  total throughput with 1 station: 250Mbps TCP throughput,
>> total with 50 stations:  225 Mbps, and with 128 stations: 20-40Mbps (it varies a lot..not so sure why).
>>
>> I poked around in the rx logic and it seems the rx-data path is fairly
>> clean for data packets.  But, from what I can tell, each beacon is going
>> to cause an skb_copy() call and a queued work-item for each station interface,
>> and there are going to be lots of beacons per second in most scenarios...
>>
>> I was wondering if this could be optimized a bit to special case beacons
>> and not make a new copy (or possibly move some of the beacon handling
>> logic up to the radio object and out of the sdata).
>>
>> And of course, it could be there are more important optimizations...I'm curious
>> if anyone is aware of any other code that should be optimized to have better
>> performance with lots of stations...
> How about doing some profiling with lots of stations - that should
> hopefully reveal where the real bottleneck is.
> By the way, with that many stations and low throughput, is the CPU usage
> on your system significantly higher, or could it just be some extra
> latency introduced somewhere else in the code?

CPU load is fairly high, but doesn't seem to just be CPU bound.  Maybe
lots and lots of work items all piled up or something like that...

I'll work on some profiling as soon as I get a chance.

I'm suspicious that the the management frame handling will
need some optimization though..I think it basically copies
the skb and broadcasts all mgt frames to all running stations....

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com