Save and close the file.

How Do I Verify Polling Settings?

To verify settings enter:

# ifconfig device
# ifconfig em0

To see MIB related to polling enter:

# sysctl -a kern.polling

Sample Output:

kern.polling.idlepoll_sleeping: 1
kern.polling.stalled: 0
kern.polling.suspect: 0
kern.polling.phase: 4
kern.polling.enable: 0
kern.polling.handlers: 2
kern.polling.residual_burst: 0
kern.polling.pending_polls: 0
kern.polling.lost_polls: 0
kern.polling.short_ticks: 0
kern.polling.reg_frac: 20
kern.polling.user_frac: 50
kern.polling.idle_poll: 0
kern.polling.each_burst: 5
kern.polling.burst_max: 150
kern.polling.burst: 150

Understanding MIB Variables

Quoting from the man page:

     kern.polling.user_frac
	     When polling is enabled, and provided that there is some work to
	     do, up to this percent of the CPU cycles is reserved to userland
	     tasks, the remaining fraction being available for polling pro-
	     cessing.  Default is 50.

     kern.polling.burst
	     Maximum number of packets grabbed from each network interface in
	     each timer tick.  This number is dynamically adjusted by the ker-
	     nel, according to the programmed user_frac, burst_max, CPU speed,
	     and system load.

     kern.polling.each_burst
	     The burst above is split into smaller chunks of this number of
	     packets, going round-robin among all interfaces registered for
	     polling.  This prevents the case that a large burst from a single
	     interface can saturate the IP interrupt queue
	     (net.inet.ip.intr_queue_maxlen).  Default is 5.

     kern.polling.burst_max
	     Upper bound for kern.polling.burst.  Note that when polling is
	     enabled, each interface can receive at most (HZ * burst_max)
	     packets per second unless there are spare CPU cycles available
	     for polling in the idle loop.  This number should be tuned to
	     match the expected load (which can be quite high with GigE
	     cards).  Default is 150 which is adequate for 100Mbit network and
	     HZ=1000.

     kern.polling.idle_poll
	     Controls if polling is enabled in the idle loop.  There are no
	     reasons (other than power saving or bugs in the scheduler's han-
	     dling of idle priority kernel threads) to disable this.

     kern.polling.reg_frac
	     Controls how often (every reg_frac / HZ seconds) the status reg-
	     isters of the device are checked for error conditions and the
	     like.  Increasing this value reduces the load on the bus, but
	     also delays the error detection.  Default is 20.

     kern.polling.handlers
	     How many active devices have registered for polling.

     kern.polling.enable
	     Legacy MIB, that was used to enable or disable polling globally.
	     Currently if set to 1, polling is enabled on all capable inter-
	     faces.  If set to 0, polling is disabled on all interfaces.

How Do I Verify Interrupt Usage Dropped Or Not?

Run top command on both server and look for interrupt line in output:

# top

How Do I Test Network Throughput?

Install iperf, enter:

# portsnap fetch update
# cd /usr/ports/benchmarks/iperf
# make install clean && rehash

After polling is enabled, use iperf tool for measuring the maximum data throughput rate of a communications link or network access. On server start iperf as follows:

# iperf -s -B 10.21.111.100 

On client type the same command as follows:

# iperf -c 10.21.111.100  -d -t 60 -i 10

• -s : run in server mode
• -B : IP bind to IP
• -c IP : run in client mode, connecting to IP
• -d : Do a bidirectional test simultaneously
• -t 60 : time in 60 seconds to transmit for.
• -i 10 : pause 10 seconds between periodic bandwidth reports.

Test Results

After enabling polling you should see nice performance increase while large number of clients connects to server under heavy load. My testing result between two WAN links connected via 10Mbits/sec metro Ethernet network:

You can clearly see increased network throughput while RX CPU load went down while using network polling.

Recommended readings:

1. The official iperf project home page.
2. man pages - iperf, polling(4) and ifconfig