Linux shaping packet loss

Simon Horman horms at verge.net.au
Wed Dec 9 01:07:53 UTC 2009


On Tue, Dec 08, 2009 at 03:14:01PM +0000, Chris wrote:
> Thanks, Steiner and everyone for the input. It's good to see the list is
> still as friendly as ever.
> 
> There are two paths I'm trying to get my head round after someone offlist
> helpfully suggested putting cburst and burst on all classes.
> 
> My thoughts are that any dropped packets on the parent class is a bad thing:
> 
> qdisc htb 1: root r2q 10 default 265 direct_packets_stat 448 ver 3.17
>  Sent 4652558768 bytes 5125175 pkt (dropped 819, overlimits 10048800
> requeues 0)
>  rate 0bit 0pps backlog 0b 28p requeues 0
> 
> Until now I've had Rate and Ceil at the same values on all the classes but I
> take the point about cburst and burst allowing greater levels of borrowing
> so I've halved the Rate for all classes and left the Ceil the same.
> 
> I've gone done this route mainly because I really can't risk breaking things
> with incorrect cburst and burst values (if anyone can please tell me on an
> i686 box at, say, 10Mbps the ideal values I can translate them into higher
> classes, TC seems to work them out as 1600b/8 mpu by default and the timing
> resolution confuses me.)

Silly question, but are you leaving some headroom?

Its a little while since I've worked with HTB and
from my experience the exact results do depend somewhat
on the kernel that is in use, but trying to use much
more than 90% of the link capacity caused troubles for me.
In particular I'm referring to the ceil value of the root class.

I also noticed that at higher packet rates (I was doing gigabit in a lab)
that increasing r2q helped me. However I was looking at (UDP) throughput
not packet loss.





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