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Date: Fri, 29 Sep 2006 15:54:35 -0700
From: "Jack Vogel" <jfvogel@gmail.com>
To: "Andrew Gallatin" <gallatin@cs.duke.edu>
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Cc: freebsd-net@freebsd.org, freebsd-current@freebsd.org,
	Andre Oppermann <andre@freebsd.org>
Subject: Re: Much improved sosend_*() functions
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On 9/29/06, Andrew Gallatin <gallatin@cs.duke.edu> wrote:
>
> Andre Oppermann writes:
>  > Andrew Gallatin wrote:
>  > > Andre,
>  > >
>  > > I meant to ask: Did you try 16KB jumbos?  Did they perform
>  > > any better than page-sized jumbos?
>  >
>  > No, I didn't try 16K jumbos.  The problem with anything larger than
>  > page size is that it may look contigous in kernel memory but isn't
>  > in physical memory.  Thus you need the same number of descriptors
>  > for the network card as with page sized (4K) clusters.
>
> But it would allow you to do one copyin, rather than 4.   I
> don't know how much this would help, but it might be worth
> looking at.

There is another limitation, due to hardware FIFO size, TSO must
never have more than 4K per descriptor. But as Andrew says, that
needn't limit you up above, it will just get parceled up in the driver.

Jack