[ath9k-devel] AR9280 DFS -- high latency

[ath9k-devel] AR9280 DFS -- high latency

[Mihai Moldovan]

Hi,

I booted up a brand new 3.10.1 kernel with DFS support enabled and obviously in use.
This AR9280 card is in AP mode on channel 40 (5GHz) with 802.11n/HT on (HT40-).

However, this boosts up latency to 50 - 90ms on average in pretty much idle mode
(100KB/s traffic), spiking up to several hundred ms to one second at times.
Maximum throughput is about 8 MBit/s with DFS, too.

Turning DFS off yields 0.x to 1ms latency and about 45 MBit/s throughput.

Is DFS still very experimental and that's the price for turning it on and
constant scanning, or does it rather sound like a bug?

Best regards,



Mihai

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[ath9k-devel] AR9280 DFS -- high latency

[Bruno Alexandre Taraio dos Santos Antunes]

Hi Mihai,

Could you or anybody in the mailing list please tell me what are the steps to enable DFS.
I?ve compiled the trunk for openwrt, all the needed files are there, but still no luck.
How is DFS enabled in openwrt?

Thanks,
Bruno

On 15 Jul, 2013, at 4:29 AM, Mihai Moldovan <ionic@ionic.de> wrote:

> Hi,
> 
> I booted up a brand new 3.10.1 kernel with DFS support enabled and obviously in use.
> This AR9280 card is in AP mode on channel 40 (5GHz) with 802.11n/HT on (HT40-).
> 
> However, this boosts up latency to 50 - 90ms on average in pretty much idle mode
> (100KB/s traffic), spiking up to several hundred ms to one second at times.
> Maximum throughput is about 8 MBit/s with DFS, too.
> 
> Turning DFS off yields 0.x to 1ms latency and about 45 MBit/s throughput.
> 
> Is DFS still very experimental and that's the price for turning it on and
> constant scanning, or does it rather sound like a bug?
> 
> Best regards,
> 
> 
> 
> Mihai
> 
> _______________________________________________
> ath9k-devel mailing list
> ath9k-devel at lists.ath9k.org
> https://lists.ath9k.org/mailman/listinfo/ath9k-devel

[ath9k-devel] AR9280 DFS -- high latency

[Mihai Moldovan]

Hi Bruno,

* On 16.08.2013 05:59 PM, Bruno Alexandre Taraio dos Santos Antunes wrote:
> Could you or anybody in the mailing list please tell me what are the steps to enable DFS.

DFS has to be enabled on the kernel side and it's dependent on an option called
CFG80211_CERTIFICATION_ONUS which is only to be enabled iff your whole system is
"regulatory compliant" even with the options enabled by that (currently DFS only
for ath9k, I guess) option. Those additional options may or may not be
regulatory compliant for the time being.

This said, once CFG80211_CERTIFICATION_ONUS has been enabled and if your kernel
is recent enough (>= 3.10), you'll be able to enable DFS in the ath9k options
tree, the symbol for that is ATH9K_DFS_CERTIFIED.

Minding all of the above, I don't think OpenWrt has support for it... yet. Those
are fragile options when it comes to compliance and OpenWrt must make sure to be
regulatory compliant on a cross-device level, so hacks like that are likely
disabled for good for now and can only be turned on by manually configuring the
kernel.

This said, hostapd probably needs DFS support as well, and to the best of my
knowledge, only the git branch of hostapd has initial (read: incomplete) DFS
support. Again, I figure OpenWrt is packaging an older stable release version,
so using DFS may prove difficult.

Why do you even want to jump through all those hoops? It's probably not worth
it, at this stage of development. Also note the performance problems I encountered.

Best regards,


Mihai

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[ath9k-devel] AR9280 DFS -- high latency

[Adrian Chadd]

...

Just for your reference - even once you enable DFS, you still have to get
it regulatory certified. No, enabling it isn't enough.

CERTIFICATION_ONUS means "it's up to me to go and get this device actually
certified and yes I will and have done this."



-adrian
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[ath9k-devel] AR9280 DFS -- high latency

[Mihai Moldovan]

* On 19.08.2013 05:25 PM, Adrian Chadd wrote:
> CERTIFICATION_ONUS means "it's up to me to go and get this device actually
> certified and yes I will and have done this."

That exactly what I meant. Thanks for clarifying that. :)

I figure OpenWrt won't support options like this officially as well, as they are
a distro supported on many devices in many different countries and aim to be as
regulatory compliant as possible.

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