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Message-ID: <20141001223229.6cbaac07@redhat.com>
Date: Wed, 1 Oct 2014 22:32:29 +0200
From: Jesper Dangaard Brouer <brouer@...hat.com>
To: Jamal Hadi Salim <jhs@...atatu.com>
Cc: Tom Herbert <therbert@...gle.com>,
David Miller <davem@...emloft.net>,
Linux Netdev List <netdev@...r.kernel.org>,
Eric Dumazet <eric.dumazet@...il.com>,
Hannes Frederic Sowa <hannes@...essinduktion.org>,
Florian Westphal <fw@...len.de>,
Daniel Borkmann <dborkman@...hat.com>,
Alexander Duyck <alexander.duyck@...il.com>,
John Fastabend <john.r.fastabend@...el.com>,
Dave Taht <dave.taht@...il.com>,
Toke Høiland-Jørgensen
<toke@...e.dk>, brouer@...hat.com
Subject: Re: [net-next PATCH V5] qdisc: bulk dequeue support for qdiscs with
TCQ_F_ONETXQUEUE
On Wed, 01 Oct 2014 16:05:31 -0400
Jamal Hadi Salim <jhs@...atatu.com> wrote:
> On 10/01/14 15:47, Jesper Dangaard Brouer wrote:
>
> >
> > Answer is yes. It is very easy with simple netperf TCP_STREAM to cause
> > queueing >1 packet in the qdisc layer.
>
> If that is the case, I withdraw any doubts i had.
> Can you please specify this in your commit logs for patch 0?
I'll try to make it more explicit.
Will resubmit patchset shortly...
Notice it is not difficult cause a queue to form, but it is tricky (not
difficult) to correctly test this patchset. Perhaps you misread my
statement earlier as "it was difficult to test and cause a queue to form"?
> > If tuned (according to my blog,
> > unloading netfilter etc.) then a single netperf TCP_STREAM will max out
> > 10Gbit/s and cause a standing queue.
> >
>
> You should describe such tuning in the patch log (hard to read
> blogs for more than 30 seconds; write a paper if you want to provide
> more details).
I think you could read this blog in 30 sec:
http://netoptimizer.blogspot.dk/2014/04/basic-tuning-for-network-overload.html
My cover letter and testing section... will take you longer that 30
sec, it have grown quite large (and Eric will not even read it :-P ;-))
Believe or not, I've actually restricted and reduced the testing
section. If you want the hole verbose version of my testing for the
upcoming V6 patch, look at this:
http://people.netfilter.org/hawk/qdisc/measure12_internal_V6_patch/
http://people.netfilter.org/hawk/qdisc/measure13_V6_patch_NObulk/
And use netperf-wrapper to dive into the data.
A quick setup guide:
http://netoptimizer.blogspot.dk/2014/09/mini-tutorial-for-netperf-wrapper-setup.html
> > I'm monitoring backlog of qdiscs, and I always see >1 backlog, I never
> > saw a standing queue of 1 packet in my testing. Either the backlog
> > area is high 100-200 packets, or 0 backlog. (With fake pktgen/trafgen
> > style tests, it's possible to cause 1000 backlog).
>
> It would be nice to actually collect such stats. Monitoring the backlog
> via dumping qdisc stats is a good start - but actually keeping traces
> of average bulk size is more useful.
I usually also monitors the BQL limits during these tests.
grep -H . /sys/class/net/eth4/queues/tx-*/byte_queue_limits/{inflight,limit}
To Toke:
Perhaps we could convince Toke, to add a netperf-wrapper recorder for
the BQL inflight and limit? (It would be really cool to plot together)
--
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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