netdev - Re: Horrid balance-rr bonding udp throughput

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Date:   Tue, 11 Apr 2017 10:28:24 -0400
From:   Jarod Wilson <jarod@...hat.com>
To:     netdev <netdev@...r.kernel.org>
Subject: Re: Horrid balance-rr bonding udp throughput

On 2017-04-10 2:50 PM, Jarod Wilson wrote:
> On 2017-04-08 7:33 PM, Jarod Wilson wrote:
>> I'm digging into some bug reports covering performance issues with 
>> balance-rr, and discovered something even worse than the reporter. My 
>> test setup has a pair of NICs, one e1000e, one e1000 (but dual e1000e 
>> seems the same). When I do a test run in LNST with bonding mode 
>> balance-rr and either miimon or arpmon, the throughput of the 
>> UDP_STREAM netperf test is absolutely horrible:
>>
>> TCP: 941.19 +-0.88 mbits/sec
>> UDP: 45.42 +-4.59 mbits/sec
>>
>> I figured I'd try LNST's packet capture mode, so exact same test, add 
>> the -p flag and I get:
>>
>> TCP: 941.21 +-0.82 mbits/sec
>> UDP: 961.54 +-0.01 mbits/sec
>>
>> Uh. What? So yeah. I can't capture the traffic in the bad case, but I 
>> guess that gives some potential insight into what's not happening 
>> correctly in either the bonding driver or the NIC drivers... More 
>> digging forthcoming, but first I have a flooded basement to deal with, 
>> so if in the interim, anyone has some insight, I'd be happy to hear 
>> it. :)
> 
> Okay, ignore the bit about bonding, I should have eliminated the bond 
> from the picture entirely. I think the traffic simply ended up on the 
> e1000 on the non-capture test and on the e1000e for the capture test, as 
> those numbers match perfectly with straight NIC to NIC testing, no bond 
> involved. That said, really odd that the e1000 is so severely crippled 
> for UDP, while TCP is still respectable. Not sure if I have a flaky NIC 
> or what...
> 
> For reference, e1000 to e1000e netperf:
> 
> TCP_STREAM: Measured rate was 849.95 +-1.32 mbits/sec
> UDP_STREAM: Measured rate was 44.73 +-5.73 mbits/sec

The rabbit hole went even deeper. The actual problem was with the ITE 
8893 PCIe bridge in the host not properly exposing capabilities, which 
required a pci quirk identical to that of the ITE 8892 to work around. 
With that in place, throughput on this venerable old e1000 goes back up 
to a reasonable 900 mbits/sec, give or take.

-- 
Jarod Wilson
jarod@...hat.com