Setting Receive Packet Steering (RPS) for 32 cores

Question

I am not sure that I used the correct commands for setting the RPS for a 32 cores machine. This is what I used: echo 1f > /sys/class/net/eth0/queues/rx-0/rps_cpus

Should it be "echo 1f..." or "echo f..." or anything else?

Answer 1

Pinterest engineers just say:

echo f > /sys/class/net/eth0/queues/rx-0/rps_cpus

But there are another their talk:

echo ffff > /sys/class/net/eth0/queues/rx-0/rps_cpus

Can't see the actual difference from kernel point of view but you can try both

Answer 2

Reproducing from the Performance Tuning Guide for Red Hat Enterprise Linux 7:

The rps_cpus files use comma-delimited CPU bitmaps. Therefore, to allow a CPU to handle interrupts for the receive queue on an interface, set the value of their positions in the bitmap to 1. For example, to handle interrupts with CPUs 0, 1, 2, and 3, set the value of rps_cpus to 00001111 (1+2+4+8), or f (the hexadecimal value for 15).

So for quad-core cpus...

echo f > /sys/class/net/eth0/queues/rx-0/rps_cpus

and for cpus with >4 cores...

echo ff+ > /sys/class/net/eth0/queues/rx-0/rps_cpus

where ff+ is a regex for appending extra f(s) for each set of additional 4 cores

Answer 3

You might want to try using binary calculator and nproc:

echo "obase=16;2^$(nproc)-1" | bc > /sys/class/net/eth0/queues/rx-0/rps_cpus

That formula will configure RPS for any number of cores.