Question about ath10k throughput
greearb at candelatech.com
Tue Apr 21 16:15:53 PDT 2015
On 04/21/2015 04:07 PM, Shu, Nick wrote:
> Hi, Ben:
> The data packet do go through the wifi interface twice, so I times 2.
> Its hard to put DUT into the chamber, cause its too big.
> I'm using your patched driver and firmware, that disabled HW encryption, so you said this will add CPU load?
> Our application can be set to run traffic in one direction, so I will test again to check the throughout in downlink, uplink, and bidirection for comparison.
> Will also try different AP, NetGear 1900 and Asus one.
In general, bi-directional traffic on wifi is a lot slower than uni-directional,
even if you add up both directions in bi-directional traffic.
I think this is mostly because the AP and station radios contend for airtime, and
you end up taking less advantage of block-acks and A-MPDUS. Maybe more retransmits
and backoffs too.. Maybe others will have a better idea.
Disabling HW encryption makes the CPU do the decryption, so yeah, that is CPU intensive.
'perf top' or similar should show your cpu usage hotspots.
> From: Ben Greear [greearb at candelatech.com]
> Sent: Tuesday, April 21, 2015 4:17 PM
> To: Shu, Nick
> Cc: ath10k at lists.infradead.org
> Subject: Re: Question about ath10k throughput
> On 04/21/2015 02:59 PM, Shu, Nick wrote:
>> Thanks, Ben:
>> We use our test application to generate traffic (TCP or UDP), sending from wifi NIC (ONLY 1 CLIENT, not multiple vStas). RF cables are used to connect from NIC antenna port (x3) to Cisco AP (model#3702E) antenna port (AP is placed inside an isolation chamber). Scan results for that AP shows the signal strength is -18 dBm (strong enough).
>> AP is connected back to test server through Ethernet cable, then Network host is route back the data packet to test application.
>> So the data throughput is calculated as: number of bytes * 2 (round trip) * 8 = Mbps.
>> So far, we can only get like 400-500 Mbps for UDP.
>> Should we set AP to open? Without encryption?
> I don't see why you do the 2x to get 'round-trip'...I think for issues related
> to wifi throughput, just talk about the amount of data flowing across the
> wifi network interface itself.
> Receiving on a station (download), when using CT firmware and with sw-crypt enabled,
> does decryption on the CPU, and this is normally a CPU bound issue at around
> 500Mbps even on expensive E5 processors.
> Upload uses HW encryption, so should run faster with modest host CPU usage.
> I would try Open auth testing when verifying wifi throughput..then compare that
> against your encrypted throughput to see if you are CPU bound (or, at least
> not RF bound).
> If you are doing true TCP protocol, then it will back off on drops (and require
> TCP ack frames and so forth). You will get quite a bit more bulk throughput
> with UDP.
> I would also try multiple different APs to try to find the best one.
> Big expensive names on the AP don't always mean so much for basic throughput
> tests in our experience.
> Having the AP inside an isolation chamber is helpful, but you really
> need your station system inside a chamber as well for a truly isolated test, otherwise
> the station system may be picking up interference that causes lost frames
> and so forth (and AP might pick up similar interference through cables
> connected to your test equipment).
> Ben Greear <greearb at candelatech.com>
> Candela Technologies Inc http://www.candelatech.com
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Candela Technologies Inc http://www.candelatech.com
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