[Codel] [PATCH net-next] codel: use Newton method instead of sqrt() and divides

[Eric Dumazet]

On Sun, 2012-05-13 at 23:00 -0700, dave taht wrote:
> I am sitting here with the latest fq_codel implementation on cerowrt, and
> this new 16 bit change.
> 
> With either interface, running netserver on the router, I get 
> ~260Mbit/sec out of it,
> with fq_codel on. It's quite marvelous, as ping times stay in the 2-3ms 
> range...
> 

If you disable TSO and GSO, do you still get good numbers ?

> Running traffic through the router with two fq_codels is another story.
> 
> I get only 91.6Mbit out of it (and the cpu on the router is loafing). I 
> was rather puzzled as
> this is sooclose to 100Mbit as for me to assume that I had goofed and 
> was running
> at line rate, but no, I'm at gigE on both sides.
> 
> A) Scheduler granularity? HZ_256 and NO_HZ here. Not sure of the clock res

fq_codel has no HZ dependencies. (it uses ktime_get())

But are you using fq_codel alone (as the root qdisc), or as leaves in a
more complex tree ?

> B) The new error in the new sqrt routine actually significant enough to 
> show up
> 
> I will try a 20ms target and revert to the previous fuller precision 
> version. I wish I had data on the previous version but was battling an 
> entirely different bug, then.
> 
> Has anyone hooked up a chain of codel ns3 sims to each other?
> 
> Or a few gigE boxes through each other?