Re: ath5k IBSS mode high latency

[Arnd Hannemann <hannemann@nets.rwth-aachen.de>]

Am 03.03.2010 18:06, schrieb Bob Copeland:
> On Tue, Mar 2, 2010 at 11:07 AM, Arnd Hannemann
> <hannemann@nets.rwth-aachen.de> wrote:
>> Hi,
>>
>> I'm currently experimenting with ath5k of kernel 2.6.33 in our
>> mesh network. We, were previously using madwifi in "ahdemo" mode,
>> which worked reasonably well.
>>
>> At the same time there is no reasonable traffic that justifies this high backlog.
>> I'm not yet sure, but it may be related to this message in dmesg:
>>
>> [ 3681.006797] ath5k phy0: no further txbuf available, dropping packet
> 
> It's likely.
> 
> When this happens, we tell mac80211 to stop all of the
> tx queues -- regardless of which queue stopped -- until
> the hardware interrupts begin processing tx status
> descriptors.  We re-enable them when there is a certain
> amount of headroom.
> 
>> Any idea how to debug this problem further?
> 
> I would add a printk to where the queues are stopped
> and re-enabled, and when packets are queued, to determine
> which queue is using up all of the descriptors.  I can put
> together a patch with the appropriate debug for you if you
> like, but in a day or two when I'm a bit less busy.

That would be nice.
However, I have to wait until saturday to get access
to the testbed again...

> 
> By the way, I did notice that if we fail to map DMA
> buffers we can leak tx descriptors, but this is unlikely
> to be the cause.
> 

Best regards,
Arnd