Date: Fri, 12 Jul 2002 07:38:42 -0400 From: Bosko Milekic <bmilekic@unixdaemons.com> To: Alfred Perlstein <bright@mu.org> Cc: Julian Elischer <julian@elischer.org>, Archie Cobbs <archie@dellroad.org>, Luigi Rizzo <rizzo@icir.org>, freebsd-net@FreeBSD.ORG Subject: Re: mbuf external buffer reference counters Message-ID: <20020712073842.A75547@unixdaemons.com> In-Reply-To: <20020712071041.GH97638@elvis.mu.org>; from bright@mu.org on Fri, Jul 12, 2002 at 12:10:41AM -0700 References: <20020712064104.GG97638@elvis.mu.org> <Pine.BSF.4.21.0207112343380.50154-100000@InterJet.elischer.org> <20020712071041.GH97638@elvis.mu.org>
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On Fri, Jul 12, 2002 at 12:10:41AM -0700, Alfred Perlstein wrote:
> * Julian Elischer <julian@elischer.org> [020712 00:00] wrote:
> >
> >
> > On Thu, 11 Jul 2002, Alfred Perlstein wrote:
> > >
> > > That's true, but could someone explain how one can safely and
> > > effeciently manipulate such a structure in an SMP environment?
> >
> > what does NetBSD do for that?
>
> They don't!
>
> *** waves skull staff exasperatedly ***
>
> RORWLRLRLLRL
Again, Alfred is right. :-)
I can't think of a way to ensure that the owner of the other mbuf
doesn't manipulate its two forward/backward pointers while we're
manipulating ours. The only way that springs to mind is to have them
protected by a mutex, but:
1) that would be very expensive and would bloat the mbuf structure a
LOT;
2) we would probably run into lock order reversal problems.
I see now what Alfred meant when he made his original comment.
--
Bosko Milekic
bmilekic@unixdaemons.com
bmilekic@FreeBSD.org
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