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Date:      Fri, 12 Jul 2002 22:08:07 -0400 (EDT)
From:      Andrew Gallatin <gallatin@cs.duke.edu>
To:        Bosko Milekic <bmilekic@unixdaemons.com>
Cc:        Julian Elischer <julian@elischer.org>, freebsd-net@FreeBSD.ORG
Subject:   Re: mbuf external buffer reference counters
Message-ID:  <15663.35719.282690.983639@grasshopper.cs.duke.edu>
In-Reply-To: <20020712213737.A7548@unixdaemons.com>
References:  <20020712122811.GA52803@hades.hell.gr> <Pine.BSF.4.21.0207121108270.50700-100000@InterJet.elischer.org> <15663.24169.445698.304534@grasshopper.cs.duke.edu> <20020712213737.A7548@unixdaemons.com>

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Bosko Milekic writes:
<...>
 >   If we decide to allocate jumbo bufs from their own seperate map as
 >   well then we have no wastage for the counters for clusters if we keep
 >   them in a few pages, like in -STABLE, and it should all work out fine.

That sounds good.

 >   For the jumbo bufs I still maintain that we should keep the counter
 >   for them at the end of the buf because the math works out (see my post
 >   in that thread with the math example) and because their total size is
 >   not a power of 2 anyway.  They'll also be more randomly spread out and
 >   use more cache slots.

How about, as (I think it was) John suggested, putting the counters at
the front of the buffer so they'd be close to the headers, etc in the
cache and would be less likely to cause their own unique cache miss
when you access them?

Drew



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