Re: high RTT in 40 MHz channel width

From: Ben Greear <greearb@candelatech.com>
To: "\"Jose Núñez-Martínez (CTTC)\"" <jose.nunez@cttc.cat>,
	"Iñaki Pascual" <ipascual@cttc.cat>,
	ath10k@lists.infradead.org
Subject: Re: high RTT in 40 MHz channel width
Date: Sat, 30 Apr 2016 09:50:53 -0700	[thread overview]
Message-ID: <5724E26D.1030103@candelatech.com> (raw)
In-Reply-To: <5724DFBB.7000208@cttc.cat>

Since UDP seems to mostly not be effected, maybe it has something
to do with your tcp stack and/or congestion control?

You could sniff on the wlan0 interface, as well as on-air, and compare timestamps
to see if the firmware is being slow about putting the TCP frames on the
air?

What TCP congestion control are you using?

And also, if there is any interference on the secondary channels, the NIC will hold
off transmitting.  So, you would not even see retransmits in this case.

Have you tried in regular managed mode (AP/STA) to see if it is the same with CT firmware?

You could try stock firmware in AP/STA mode.  If CT firmware shows
a regression, I will be happy to look at it.

Finally, you might try the latest CT firmware in case it acts better.  I
ripped out some queue control in the non-full builds somewhat recently,
and possibly that would decrease latency.

Thanks,
Ben

On 04/30/2016 09:39 AM, Jose Núñez-Martínez (CTTC) wrote:
> Hi all,
> just to clarify, results are ms. And stations are in IBSS mode.
>
> BW 20 MHz: TCP 0.9ms UDP 1.1ms
> BW 40 MHz: TCP 7.7ms UDP 1.3ms
> BW 80 MHz: TCP 3.5ms UDP 1.3ms
>
> Behavior with 40MHz and 80MHz channel bandwidth is really weird taking into account there are no retransmissions. Anyone facing this kind of problem?
>
> Thanks,
> Jose
>
> On 04/29/2016 07:12 PM, Iñaki Pascual wrote:
>> Hi,
>>
>> I am measuring TCP and UDP latency (actually RTT) and I am getting too high values when working with channels with 40MHz (also with 80MHz) width.
>>
>> I am using hping3 for testing and these are the RTT avg values:
>>
>> BW 20 MHz: TCP 0.9 UDP 1.1
>> BW 40 MHz: TCP 7.7 UDP 1.3
>> BW 80 MHz: TCP 3.5 UDP 1.3
>>
>> I have tried different channels with similar results. According hping there are no packet loss and with wireshark I don't see any retransmission.
>>
>> I am using:
>> driver: ath10k_pci
>> version: 4.2.0+
>> firmware-version: 10.1.467-ct-com-full-014-96d543
>>
>> Any ideas?
>>
>> Bests,
>>
>> Iñaki
>>
>> _______________________________________________
>> ath10k mailing list
>> ath10k@lists.infradead.org
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>

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

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