Re: Multiple vifs and HT v/s non-HT.

[Ben Greear <greearb@candelatech.com>]

On 01/28/2011 05:17 AM, Johannes Berg wrote:
> On Thu, 2011-01-27 at 15:07 -0800, Ben Greear wrote:
>> We found something fun while playing with HT mode:
>>
>> We had some vifs associated with an AP with HT enabled,
>> and other VIFS to an AP with HT disabled.
>>
>> They managed to associate, but with slow rates and
>> for whatever reason, nothing is able to send traffic.
>> I would have expected one set or the other would
>> be able to send traffic.
>>
>> The ath9k hardware ended up in HT mode according to
>> ath9k debugfs wiphy file, but that was probably
>> just luck.
>>
>> I'm not too sure how to ensure this mixed-mode HT
>> scenario doesn't happen at this point...
>
> So that patch you sent addressed this?

Well, I could no longer (easily?) reproduce the problem,
but to be honest, I don't see how my changes could have fixed
the problem that I saw.  I still think that patch is useful
and could fix other problems, however.

I ran 30 STAs w/out HT and 30 with all night, about 175kbps UDP tx + rx on
each interface, and it ran OK.

But, there may still be issues/races with initial setup and state transitions.

At the least, the set-channel-type method should do WARN_ON_ONCE
instead of WARN_ON if you have HT40+ on some VIFs and HT40-
on others.  I was also thinking that the first vif(s) to associate
on a channel-type should win..and just fail to set the channel type
to something invalid (ie, ht40- -> ht40+) in that case.  Otherwise,
I think you would get endless flapping.

Thanks,
Ben

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