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

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Message-ID: <1410801863.7106.169.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 15 Sep 2014 10:24:23 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	Jesper Dangaard Brouer <brouer@...hat.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, 2014-09-15 at 10:10 -0700, Tom Herbert wrote:
> 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.

Right.

Jesper, relevant netperf option is :

    -y local,remote   Set the socket priority


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