Receive Packet Steering (RPS) on Linux 2.6.35

This patch implements software receive side packet steering (RPS). RPS distributes the load of received packet processing across multiple CPUs. Problem statement: Protocol processing done in the NAPI context for received packets is serialized per device queue and becomes a bottleneck under high packet load. This substantially limits pps that can be achieved on a single queue NIC and provides no scaling with multiple cores. (lwn.net: Software receive packet steering)

If you want to find out whether RPS is working, you have to look at /proc/softirqs instead (eg. with watch -n1 cat /proc/softirqs):

                CPU0       CPU1

       HI:          0          0

    TIMER:  480622794  476948579

   NET_TX:   25311134   27075847     <-----

   NET_RX: 1388399338 4191697027     <-----

    BLOCK:    4632803          3

 BLOCK_IOPOLL:          0          0

  TASKLET:         21          4

    SCHED:  154913375  158601463

  HRTIMER:    1576760    2361409

      RCU:  421549961  407634645 

Enabling RPS specifically for a particular interface:

# cat /sys/class/net/eth0/queues/rx-0/rps_cpus 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,00000000  # echo f > /sys/class/net/eth0/queues/rx-0/rps_cpus # cat /sys/class/net/eth0/queues/rx-0/rps_cpus 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000, 00000000,00000000,00000000,00000000,00000000,00000000,0000000f