Subject: Qdisc: Measuring Head-of-Line blocking with netperf-wrapper

From: Jesper Dangaard Brouer <[email-masked]>
Date: Mon, 15 Sep 2014 18:45:17 +0200

Hi Eric,

I've constructed a "netperf-wrapper" test for measuring Head-of-Line
blocking, called "tcp_upload_prio", that I hope you will approve of?

 https://github.com/tohojo/netperf-wrapper/commit/1e6b755e8051b6

The basic idea is to have ping packets with TOS bit 0x10, which end-up
in the high-prio band of pfifo_fast.  While two TCP uploads utilize
all the bandwidth.

These high-prio ping packet should then demonstrate the Head-of-Line
blocking occurring due to 1) packets in the HW TX ring buffer, or
2) in the qdisc layers requeue mechanism.  Disgusting these two case
might be a little difficult.

Special care need to be take for using this on the default
qdisc MQ which have pfifo_fast assigned for every HW queue.

Setup requirements:
 1. IRQ align CPUs to NIC HW queues
 2. Force netperf-wrapper subcommands to run the same CPU
  E.g: taskset -c 2 ./netperf-wrapper -H IP tcp_upload_prio

This will force all measurements to go through the same qdisc.  This
is needed so the ping/latency tests measures the real property of
the qdisc and Head-of-Line blocking effect.

Basically the same as:
 sudo taskset -c 2 ping -Q 0x10 192.168.8.2
 sudo taskset -c 2 ping         192.168.8.2
 sudo taskset -c 2 netperf   -H 192.168.8.2 -t TCP_STREAM -l 120
 sudo taskset -c 2 netperf   -H 192.168.8.2 -t TCP_STREAM -l 120
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer