Basically you want it to hold a number of mbufs
and you want it to fit into a page nicely.
you probably want it to have a bit of extra rume for oversized
packets too.
2K seems a good fit. nothing magic about it however.
(should be less than a page, bigget than an ehternet packet(plus a bit)
4096/3 is 1365.... too small
4096/2=2048 ok..
4096/1 too wasteful.
On Wed, 25 Jul 2001, Zhihui Zhang wrote:
>
>
> On Tue, 24 Jul 2001, Terry Lambert wrote:
>
> > Zhihui Zhang wrote:
> > > > Hi,
> > > > in freebsd can we change the cluster size from 2048
> > > > bytes.If yes how can we do that?
> > > > do we have to configure in some file?
> > >
> > > You must be asking why the mbuf cluster size is chosen as 2048, right? It
> > > is probably a tradeoff between memory efficient and speed.
> >
> > Ask yourselves:
> >
> > "What is the minimum cluster size I would have to have
> > to be able to contain the maximum MTU worth of data,
> > yet remain an even multiple of sizeof(mbuf) -- 256
> > bytes?"
>
> A dumb question: why even not odd multiple?
>
> -Zhihui
>
>
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