Hi,
lets come to my question please.
tell me can i change mbuf cluster size from 2048 to
4096??
how shd i do it if i can do it?
--- Julian Elischer <[EMAIL PROTECTED]> wrote: >
no.. it has to do with the fact that it would be
> unwise
> to make a cluster > 1 page size since we have no
> guarantee that
> all drivers could handle breaking up a DMA if a
> cluster spanned 2
> physical address ranges. (they can handle a chain of
> discontinuous
> mbufs but may assume that a single mbuf will have
> physically
> contiguous data. Now since we cannot span a page
> boundary,
> we should fit in exacly to get as much room as
> possible
> and since (pagesize/3) is too small, the next
> possibility is (pagesize/2).
>
> If pagesize/3 was big enough, we might have used
> that..
>
>
> On Wed, 25 Jul 2001, Zhihui Zhang wrote:
>
> >
> > I see. It has something to do with the
> power-of-two allocator we are
> > using inside the kernel.
> >
> > -Zhihui
> >
> > On Wed, 25 Jul 2001, Bosko Milekic wrote:
> >
> > >
> > > On Wed, Jul 25, 2001 at 01:51:51PM -0400, 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
> > >
> > > It actually has to do with the fact that 2K is
> the only size equal to
> > > or greater than the maximum MTU worth of data
> that can be multiplied to a page
> > > size without any leftover (in other words, page
> size modulo 2K is zero).
> > >
> > > --
> > > Bosko Milekic
> > > [EMAIL PROTECTED]
> > >
> > >
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> >
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