[Codel] FQ_Codel lwn draft article review

Paul E. McKenney paulmck at linux.vnet.ibm.com
Mon Nov 26 12:20:48 EST 2012

On Sat, Nov 24, 2012 at 01:07:04AM +0100, Toke Høiland-Jørgensen wrote:
> "Paul E. McKenney" <paulmck at linux.vnet.ibm.com> writes:
> > I am using these two in a new "Effectiveness of FQ-CoDel" section.
> > Chrome can display .svg, and if it becomes a problem, I am sure that
> > they can be converted.  Please let me know if some other data would
> > make the point better.
> If you are just trying to show the "ideal" effectiveness of fq_codel,
> two attached graphs are from some old tests we did at the UDS showing a
> simple ethernet link between two laptops with a single stream going in
> each direction. This is of course by no means a real-world test, but on
> the other hand they show a very visible factor ~4 improvement in
> latency.
> These are the same graphs Dave used in his slides, but also in a 100mbit
> version.
> > Also, I know what ICMP is, but the UDP variants are new to me.  Could
> > you please expand the "EF", "BK", "BE", and "CSS" acronyms?
> The UDP ping times are simply roundtrips/second (as measured by netperf)
> converted to ping times. The acronyms are diffserv markings, i.e.
> EF=expedited forwarding, BK=bulk (CS1 marking), BE=best effort (no
> marking). The UDP ping tests tend to not work so well on a loaded link,
> however, since netperf stops sending packets after detecting
> (excessive(?)) loss. Which is why you see only see the UDP ping times on
> the first part of the graph.
> The markings are also used on the TCP flows, as seen in the legend for
> the up/downloads.
> > All sessions were started at T+5, then?
> The pings start right away, the transfers start at T+5 seconds. Looks
> like the first ~five seconds of transfer is being cut off on those
> graphs. I think what happens is that one of the streams (the turquoise
> one) starts up faster than the other ones, consuming all the bandwidth
> for the first couple of seconds until they adjust to the same level.
> These initial values are then scaled off the graph as outlier values. If
> you zoom in on the beginning of the graph you can see the turquoise line
> coming down from far off the scale in one direction, while the rest come
> From off the bottom.
> > Please see attached for update including .git directory.
> I got a little lost in all the lists of SFQ, but other than that I found
> it quite readable. The diagrams of the queuing algorithms are a tad big,
> though, I think. :)

Thank you, I have shrunk the figures and added the acronym expansions.

							Thanx, Paul

> When is the article going to be published?
> -Toke
> -- 
> Toke Høiland-Jørgensen
> toke at toke.dk

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