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Re: dummy as IMQ replacement

To: Andy Furniss <andy.furniss@xxxxxxxxxxxxx>
Subject: Re: dummy as IMQ replacement
From: Thomas Graf <tgraf@xxxxxxx>
Date: Wed, 2 Feb 2005 14:28:16 +0100
Cc: jamal <hadi@xxxxxxxxxx>, netdev@xxxxxxxxxxx, Nguyen Dinh Nam <nguyendinhnam@xxxxxxxxx>, Remus <rmocius@xxxxxxxxxxxxxx>, Andre Tomt <andre@xxxxxxxx>, syrius.ml@xxxxxxxxxx, Damion de Soto <damion@xxxxxxxxxxxx>
In-reply-to: <41FF9A55.4080005@xxxxxxxxxxxxx>
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> >>WRT policers I never figured out where you would put the effects of 
> >>playing with the burst size parameter and it's effects with few/many 
> >>connections and any burstiness caused into an equasion like that.
> >
> >
> >A burst buffer has impact on R on later packets, it can "smooth" R
> >and X and thus results in more stable rates. Depending on the actual
> >burst, it can avoid retransmits which stabilizes the rate as well.
> 
> But it's not a real rate limiting buffer in the policer case is it?

Abstractly speaking, burst specifies the maximum amount of time allowed
for a single packet to sit in the burst buffer. Although the burst is
configured as the size of the buffer it is transformed into a time
delta before providing it to the kernel. Because the policer doesn't
enqueue things the packet simply gets dropped if it would exceed that
time. It's not _exactly_ like this but it gives you an idea what
happens, net/sched/police.c isn't that big so one coffee should do it.

> Nice - are you planning to add anything to tweak things for the wrong 
> end of the bottleneck problems?

I hope so, once I figured out an acceptable compromise between a good
result and simplicity. Currently it would be way to expensive and hard
to use.

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