Mellanox performance degradation with more than 12 lcores

Mellanox performance degradation with more than 12 lcores

[Дмитрий Степанов]

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Hi folks!

I'm using Mellanox ConnectX-6 Dx EN adapter card (100GbE; Dual-port QSFP56;
PCIe 4.0/3.0 x16) with DPDK 21.11 on a server with AMD EPYC 7702 64-Core
Processor (NUMA system with 2 sockets). Hyperthreading is turned off.
I'm testing the maximum receive throughput I can get from a single port
using testpmd utility (shipped with dpdk). My generator produces random UDP
packets with zero payload length.

I get the maximum performance using 8-12 lcores (overall 120-125Mpps on
receive path of single port):

numactl -N 1 -m 1 /opt/dpdk-21.11/build/app/dpdk-testpmd -l 64-127 -n 4  -a
0000:c1:00.0 -- --stats-period 1 --nb-cores=12 --rxq=12 --txq=12 --rxd=512

With more than 12 lcores overall receive performance reduces. With 16-32
lcores I get 100-110 Mpps, and I get a significant performance fall with 33
lcores - 84Mpps. With 63 cores I get even 35Mpps  overall receive
performance.

Are there any limitations on the total number of receive queues (total
lcores) that can handle a single port on a given NIC?

Thanks,
Dmitriy Stepanov

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Re: Mellanox performance degradation with more than 12 lcores

[Asaf Penso]

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Hello Dmitry,

Could you please paste the testpmd commands per each experiment?

Also, have you looked into dpdk.org performance report to see how to tune for best results?

Regards,
Asaf Penso
________________________________
From: Дмитрий Степанов <stepanov.dmit@gmail.com>
Sent: Friday, February 18, 2022 9:32:59 AM
To: users@dpdk.org <users@dpdk.org>
Subject: Mellanox performance degradation with more than 12 lcores

Hi folks!

I'm using Mellanox ConnectX-6 Dx EN adapter card (100GbE; Dual-port QSFP56; PCIe 4.0/3.0 x16) with DPDK 21.11 on a server with AMD EPYC 7702 64-Core Processor (NUMA system with 2 sockets). Hyperthreading is turned off.
I'm testing the maximum receive throughput I can get from a single port using testpmd utility (shipped with dpdk). My generator produces random UDP packets with zero payload length.

I get the maximum performance using 8-12 lcores (overall 120-125Mpps on receive path of single port):

numactl -N 1 -m 1 /opt/dpdk-21.11/build/app/dpdk-testpmd -l 64-127 -n 4  -a 0000:c1:00.0 -- --stats-period 1 --nb-cores=12 --rxq=12 --txq=12 --rxd=512

With more than 12 lcores overall receive performance reduces. With 16-32 lcores I get 100-110 Mpps, and I get a significant performance fall with 33 lcores - 84Mpps. With 63 cores I get even 35Mpps  overall receive performance.

Are there any limitations on the total number of receive queues (total lcores) that can handle a single port on a given NIC?

Thanks,
Dmitriy Stepanov

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RE: Mellanox performance degradation with more than 12 lcores

[Dmitry Kozlyuk]

Hi,

> With more than 12 lcores overall receive performance reduces.
> With 16-32 lcores I get 100-110 Mpps,

It is more about the number of queues than the number of cores:
12 queues are the threshold when Multi-Packet Receive Queue (MPRQ)
is automatically enabled in mlx5 PMD.
Try increasing --rxd and check out mprq_en device argument.
Please see mlx5 PMD user guide for details about MPRQ.
You should be able to get full 148 Mpps with your HW.

> and I get a significant performance fall with 33 lcores - 84Mpps.
> With 63 cores I get even 35Mpps overall receive performance.
> 
> Are there any limitations on the total number of receive queues (total
> lcores) that can handle a single port on a given NIC?

This is a hardware limitation.
The limit on the number of queues you can create is very high (16M),
but performance can perfectly scale only up to 32 queues
at high packet rates (as opposed to bit rates).
Using more queues can even degrade it, just as you observe.
One way to overcome this (not specific to mlx5)
is to use a ring buffer for incoming packets,
from which any number of processing cores can take packets.

Re: Mellanox performance degradation with more than 12 lcores

[Дмитрий Степанов]

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I get 125 Mpps from single port using 12 lcores:
numactl -N 1 -m 1 /opt/dpdk-21.11/build/app/dpdk-testpmd -l 64-127 -n 4  -a
0000:c1:00.0 -- --stats-period 1 --nb-cores=12 --rxq=12 --txq=12 --rxd=512

With 63 cores i get 35 Mpps:
numactl -N 1 -m 1 /opt/dpdk-21.11/build/app/dpdk-testpmd -l 64-127 -n 4  -a
0000:c1:00.0 -- --stats-period 1 --nb-cores=63 --rxq=63 --txq=63 --rxd=512

I'm using this guide as a reference -
https://fast.dpdk.org/doc/perf/DPDK_20_11_Mellanox_NIC_performance_report.pdf
This reference suggests examples of how to get the best performance but all
of them use maximum 12 lcores.
125 Mpps with 12 lcores is nearly the maximum I can get from single 100GB
port (148Mpps theoretical maximum for 64byte packet). I just want to
understand - why I get good performance with 12 lcores and bad performance
with 63 cores?

пт, 18 февр. 2022 г. в 16:30, Asaf Penso <asafp@nvidia.com>:

> Hello Dmitry,
>
> Could you please paste the testpmd commands per each experiment?
>
> Also, have you looked into dpdk.org performance report to see how to tune
> for best results?
>
> Regards,
> Asaf Penso
> ------------------------------
> *From:* Дмитрий Степанов <stepanov.dmit@gmail.com>
> *Sent:* Friday, February 18, 2022 9:32:59 AM
> *To:* users@dpdk.org <users@dpdk.org>
> *Subject:* Mellanox performance degradation with more than 12 lcores
>
> Hi folks!
>
> I'm using Mellanox ConnectX-6 Dx EN adapter card (100GbE; Dual-port
> QSFP56; PCIe 4.0/3.0 x16) with DPDK 21.11 on a server with AMD EPYC 7702
> 64-Core Processor (NUMA system with 2 sockets). Hyperthreading is turned
> off.
> I'm testing the maximum receive throughput I can get from a single port
> using testpmd utility (shipped with dpdk). My generator produces random UDP
> packets with zero payload length.
>
> I get the maximum performance using 8-12 lcores (overall 120-125Mpps on
> receive path of single port):
>
> numactl -N 1 -m 1 /opt/dpdk-21.11/build/app/dpdk-testpmd -l 64-127 -n 4
>  -a 0000:c1:00.0 -- --stats-period 1 --nb-cores=12 --rxq=12 --txq=12
> --rxd=512
>
> With more than 12 lcores overall receive performance reduces. With 16-32
> lcores I get 100-110 Mpps, and I get a significant performance fall with 33
> lcores - 84Mpps. With 63 cores I get even 35Mpps  overall receive
> performance.
>
> Are there any limitations on the total number of receive queues (total
> lcores) that can handle a single port on a given NIC?
>
> Thanks,
> Dmitriy Stepanov
>

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Re: Mellanox performance degradation with more than 12 lcores

[Дмитрий Степанов]

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Thanks for the clarification!
I was able to get 148Mpps with 12 lcores after some BIOS tunings.
Looks like due to these HW limitations I have to use ring buffer as you
suggested to support more than 32 lcores!

пт, 18 февр. 2022 г. в 16:40, Dmitry Kozlyuk <dkozlyuk@nvidia.com>:

> Hi,
>
> > With more than 12 lcores overall receive performance reduces.
> > With 16-32 lcores I get 100-110 Mpps,
>
> It is more about the number of queues than the number of cores:
> 12 queues are the threshold when Multi-Packet Receive Queue (MPRQ)
> is automatically enabled in mlx5 PMD.
> Try increasing --rxd and check out mprq_en device argument.
> Please see mlx5 PMD user guide for details about MPRQ.
> You should be able to get full 148 Mpps with your HW.
>
> > and I get a significant performance fall with 33 lcores - 84Mpps.
> > With 63 cores I get even 35Mpps overall receive performance.
> >
> > Are there any limitations on the total number of receive queues (total
> > lcores) that can handle a single port on a given NIC?
>
> This is a hardware limitation.
> The limit on the number of queues you can create is very high (16M),
> but performance can perfectly scale only up to 32 queues
> at high packet rates (as opposed to bit rates).
> Using more queues can even degrade it, just as you observe.
> One way to overcome this (not specific to mlx5)
> is to use a ring buffer for incoming packets,
> from which any number of processing cores can take packets.
>

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