netdev - Accelerated receive flow steering (aRFS) for UDP

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Date:   Fri, 7 Oct 2016 22:55:52 +0000
From:   "Chopra, Manish" <Manish.Chopra@...ium.com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "maorg@...lanox.com" <maorg@...lanox.com>,
        "tom@...bertland.com" <tom@...bertland.com>
Subject: Accelerated receive flow steering (aRFS) for UDP

Hello Folks,

I am experimenting aRFS with our NIC devices, and for that I have kernel 4.8.x installed with below config.

CONFIG_RPS=y
CONFIG_RFS_ACCEL=y

# cat /proc/cpuinfo  | grep processor
processor       : 0
processor       : 1
processor       : 2
processor       : 3
processor       : 4
processor       : 5
processor       : 6
processor       : 7
processor       : 8
processor       : 9
processor       : 10
processor       : 11
processor       : 12
processor       : 13
processor       : 14
processor       : 15

I configured rps_sock_flow_entries  and our NIC rx queues with below values

echo 32768 > /proc/sys/net/core/rps_sock_flow_entries
echo 4096 > /sys/class/net/p4p1/queues/rx-0/rps_flow_cnt
echo 4096 > /sys/class/net/p4p1/queues/rx-1/rps_flow_cnt
echo 4096 > /sys/class/net/p4p1/queues/rx-2/rps_flow_cnt
echo 4096 > /sys/class/net/p4p1/queues/rx-3/rps_flow_cnt
echo 4096 > /sys/class/net/p4p1/queues/rx-4/rps_flow_cnt
echo 4096 > /sys/class/net/p4p1/queues/rx-5/rps_flow_cnt
echo 4096 > /sys/class/net/p4p1/queues/rx-6/rps_flow_cnt
echo 4096 > /sys/class/net/p4p1/queues/rx-7/rps_flow_cnt

echo ffff > /sys/class/net/p4p1/queues/rx-0/rps_cpus
echo ffff > /sys/class/net/p4p1/queues/rx-1/rps_cpus
echo ffff > /sys/class/net/p4p1/queues/rx-2/rps_cpus
echo ffff > /sys/class/net/p4p1/queues/rx-3/rps_cpus
echo ffff > /sys/class/net/p4p1/queues/rx-4/rps_cpus
echo ffff > /sys/class/net/p4p1/queues/rx-5/rps_cpus
echo ffff > /sys/class/net/p4p1/queues/rx-6/rps_cpus
echo ffff > /sys/class/net/p4p1/queues/rx-7/rps_cpus

Below is IRQ affinity configuration for NIC irqs used. 

# cat /proc/irq/67/smp_affinity_list
8
# cat /proc/irq/68/smp_affinity_list
9
# cat /proc/irq/69/smp_affinity_list
10
# cat /proc/irq/70/smp_affinity_list
11
# cat /proc/irq/71/smp_affinity_list
12
# cat /proc/irq/72/smp_affinity_list
13
# cat /proc/irq/73/smp_affinity_list
14
# cat /proc/irq/74/smp_affinity_list
15

Driver has required feature NETIF_F_NTUPLE set, ndo_rx_flow_steer() registered and I am running UDP multiple connections stream using netperf to the host where I am experimenting aRFS. 

# netperf -V
Netperf version 2.7.0

netperf -H 192.168.200.40 -t UDP_STREAM -l 150 -T 8,8 -- -m 1470 -P 5001,48512 &
netperf -H 192.168.200.40 -t UDP_STREAM -l 150 -T 9,9 -- -m 1470 -P 5001,37990 &
netperf -H 192.168.200.40 -t UDP_STREAM -l 150 -T 10,10 -- -m 1470 -P 5001,40302 &
netperf -H 192.168.200.40 -t UDP_STREAM -l 150 -T 11,11 -- -m 1470 -P 5001,39071 &
netperf -H 192.168.200.40 -t UDP_STREAM -l 150 -T 12,12 -- -m 1470 -P 5001,58994 &
netperf -H 192.168.200.40 -t UDP_STREAM -l 150 -T 13,13 -- -m 1470 -P 5001,59884 &
netperf -H 192.168.200.40 -t UDP_STREAM -l 150 -T 14,14 -- -m 1470 -P 5001,40282 &
netperf -H 192.168.200.40 -t UDP_STREAM -l 150 -T 15,15 -- -m 1470 -P 5001,56042 &

I see that our registered callback for ndo_rx_flow_steer() "NEVER" gets invoked for UDP packets, with TCP_STREAM I do see it gets invoked.
But while running UDP_STREAM I see it gets invoked for some of TCP packets as netperf also uses TCP managed connections while running  UDP_STREAM.

My initial investigation suspects that while running UDP_STREAM with netperf, rps_sock_flow_table doesn't get updated, as packets never reach to the flow of inet_recvmsg()
where it gets updated using sock_rps_record_flow(). Which might be the reason it never invokes NIC's flow steering handler ?

Please note that when I run UDP stream using "iperf" - I do see that our registered callback function for flow steering gets invoked for "UDP" packets.
I am not sure if I am missing something in configuration or something else which is I am unware of  ? 

I appreciate any help for this.

Thanks and Regards,
Manish Chopra