mbuf layout optimizations

[Jeff Roberson]

On Fri, 19 Jun 2009, Barney Cordoba wrote:

>
>
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> --- On Fri, 6/19/09, Jeff Roberson <jroberson at jroberson.net> wrote:
>
>> From: Jeff Roberson <jroberson at jroberson.net>
>> Subject: mbuf layout optimizations
>> To: net at freebsd.org, current at freebsd.org
>> Date: Friday, June 19, 2009, 5:12 AM
>> http://people.freebsd.org/~jeff/mbuf2.diff
>> 
>> Hello,
>> 
>> This is a call for testers and feedback on my mbuf layout
>> improvements. I'm trying to decide whether I will push to
>> have these included in 8.0. After reducing the scope
>> slightly from my last patch, I have not encountered any
>> problems.  Kip Macy has also been using it for the past
>> few weeks without issue.
>> 
>> You should not expect any functional changes from this
>> patch.  The goal is mostly to pave the way fors more
>> sensible mbuf handling in the future, although it does offer
>> a few performance benefits.
>> 
>> The only issue is that cxgb support requires another set of
>> patches from Kip.  If anyone needs those I will prod
>> him to reply with that diff.
>> 
>> Thanks,
>> Jeff
>
> I thought that the purpose of m_tags was to keep individual applications from having to "patch" mbufs. Has that idea proven to be too
> performance-challenged?

m_tags are unrelated to this diff.  This addresses the fundamental memory 
allocation mechanisms and layout of the mbuf.  It reduces the amount of 
book keeping necessary and makes reference counts more pervasive.

Thanks,
Jeff

>
> Barney
>