Unstable local network throughput

[Ben RUBSON]

> On 04 Aug 2016, at 17:33, Hans Petter Selasky <hps at selasky.org> wrote:
> 
> On 08/04/16 17:24, Ben RUBSON wrote:
>> 
>>> On 04 Aug 2016, at 11:40, Ben RUBSON <ben.rubson at gmail.com> wrote:
>>> 
>>>> On 02 Aug 2016, at 22:11, Ben RUBSON <ben.rubson at gmail.com> wrote:
>>>> 
>>>>> On 02 Aug 2016, at 21:35, Hans Petter Selasky <hps at selasky.org> wrote:
>>>>> 
>>>>> The CX-3 driver doesn't bind the worker threads to specific CPU cores by default, so if your CPU has more than one so-called numa, you'll end up that the bottle-neck is the high-speed link between the CPU cores and not the card. A quick and dirty workaround is to "cpuset" iperf and the interrupt and taskqueue threads to specific CPU cores.
>>>> 
>>>> My CPUs : 2x E5-2620v3 with DDR4 at 1866.
>>> 
>>> OK, so I cpuset all Mellanox interrupts to one NUMA, as well as the iPerf processes, and I'm able to reach max bandwidth.
>>> Choosing the wrong NUMA (or both, or one for interrupts, the other one for iPerf, etc...) totally kills throughput.
>>> 
>>> However, full-duplex throughput is still limited, I can't manage to reach 2x40Gb/s, throttle is at about 45Gb/s.
>>> I tried many different cpuset layouts, but I never went above 45Gb/s.
>>> (Linux allowed me to reach 2x40Gb/s so hardware is not a bottleneck)
>>> 
>>>>> Are you using "options RSS" and "options PCBGROUP" in your kernel config?
>>> 
>>> I will then give RSS a try.
>> 
>> Without RSS :
>> A ---> B : 40Gbps (unidirectional)
>> A <--> B : 45Gbps (bidirectional)
>> 
>> With RSS :
>> A ---> B : 28Gbps (unidirectional)
>> A <--> B : 28Gbps (bidirectional)
>> 
>> Sounds like RSS does not help :/
>> 
>> Why, without RSS, do I have difficulties to reach 2x40Gbps (full-duplex) ?
>> 
> 
> Hi,
> 
> Possibly because the packets are arriving at the wrong CPU compared to what RSS expects. Then RSS will invoke a taskqueue to process the packets on the correct CPU, if I'm not mistaken.

But even without RSS, I should be able to go up to 2x40Gbps, don't you think so ?
Nobody already did this ?