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Re: [Xen-devel] [PATCH] Increase MAX_SKBUFF_ORDER

from [Philip R. Auld]

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To:	Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>
Subject:	Re: [Xen-devel] [PATCH] Increase MAX_SKBUFF_ORDER
From:	"Philip R. Auld" <pauld@xxxxxxxxxxx>
Date:	Thu, 10 Nov 2005 16:51:37 -0500
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Hi Ian,

Rumor has it that on Thu, Nov 10, 2005 at 09:08:44PM -0000 Ian Pratt said:
>  
> >     The recent (changeset 7700) switch to use the 
> > architecture specific skbuff allocation routine breaks with 
> > very large MTU sizes.
> > The below patch raises the MAX_SKBUFF_ORDER to 3. Could this 
> > be applied to make it the default?
> 
> I suspect the only reason things worked for you before was that you were
> relying on swiotlb. (enabled if you have >2GB). I need to think through
> the implactions of changing MAX_SKBUFF_ORDER...

Can you explain the swiotlb part? The large MTUs are only on dom0.
It worked before because alloc_skb used kmalloc and gave me 
pseudo-physical contigous regions, which is sufficient. Packets 
coming from and going to domUs would all be within the first page. 
But since dom0 is receiving packets from rdma I have to post 
packets large enough to cover anything that could be sent to dom0.
And for compatibility within the system that's about 17k, 
unfortunately.

Cheers,

Phil

> 
> Ian

-- 
Philip R. Auld, Ph.D.                          Egenera, Inc.    
Software Architect                            165 Forest St.
(508) 858-2628                            Marlboro, MA 01752

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