netdev - Re: [net-next PATCH V5] qdisc: bulk dequeue support for qdiscs with TCQ_F

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Message-ID: <542C5E8B.7070204@mojatatu.com>
Date:	Wed, 01 Oct 2014 16:05:31 -0400
From:	Jamal Hadi Salim <jhs@...atatu.com>
To:	Jesper Dangaard Brouer <brouer@...hat.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>
Subject: Re: [net-next PATCH V5] qdisc: bulk dequeue support for qdiscs with
 TCQ_F_ONETXQUEUE

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?

> 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'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.

cheers,
jamal
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