netdev - Re: Qdisc: Measuring Head-of-Line blocking with netperf-wrapper

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Message-ID: <CA+mtBx_EthN8G0oEUENmVhb8MJ2MrijhT+FRjJPomBLvJPoH_w@mail.gmail.com>
Date:	Mon, 15 Sep 2014 10:10:53 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Stephen Hemminger <stephen@...workplumber.org>,
	David Miller <davem@...emloft.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Florian Westphal <fw@...len.de>,
	Toke Høiland-Jørgensen <toke@...e.dk>,
	Dave Taht <dave.taht@...il.com>
Subject: Re: Qdisc: Measuring Head-of-Line blocking with netperf-wrapper

On Mon, Sep 15, 2014 at 9:45 AM, Jesper Dangaard Brouer
<brouer@...hat.com> wrote:
>
> 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
> --
ping is a very coarse way to measure latency and in network devices it
doesn't follow same path as TCP/UDP (no 4-tuple for RSS, ECMP) so it's
biased and not a very realistic workload. You might want to try using
netperf TCP_RR at higher priority for a fairer comparison (this is
what I used to verify BQL benefits). Also, you probably want to make
sure to have enough antagonist flows to saturate all links when using
MQ.

> 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
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