Date: Thu, 11 Jul 2002 21:34:51 -0700 From: Alfred Perlstein <bright@mu.org> To: Bosko Milekic <bmilekic@unixdaemons.com> Cc: Julian Elischer <julian@elischer.org>, Luigi Rizzo <rizzo@icir.org>, freebsd-net@FreeBSD.ORG Subject: Re: mbuf external buffer reference counters Message-ID: <20020712043451.GE97638@elvis.mu.org> In-Reply-To: <20020711222725.A5284@unixdaemons.com> References: <20020711171255.A19014@unixdaemons.com> <Pine.BSF.4.21.0207111606440.47612-100000@InterJet.elischer.org> <20020711222725.A5284@unixdaemons.com>
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* Bosko Milekic <bmilekic@unixdaemons.com> [020711 19:28] wrote: > > On Thu, Jul 11, 2002 at 04:10:32PM -0700, Julian Elischer wrote: > > Don't forget that "external" does not neccesarily mean "cluster". > > I still consider the method used in (hmm was it NetBSD or OSF/1?) > > to be very good.. > > > > mbufs that referred to the same object were linked together. > > I forget the details exactly. maybe someone else can remember.. > > it did it without ref counts somehow.. > > Yes, this is in NetBSD still and it is very elegant. I remember > looking at this a long time ago but to be honest, the reason I didn't > implement it then first escaped me. However, thanks to David Malone's > awesome commit messages, I found it: > > rev 1.53 of sys/sys/mbuf.h, extract: > [...] > "NetBSD's system of linked lists of mbufs was cosidered, but Alfred > felt it would have locking issues when the kernel was made more > SMP friendly." > [...] > > I think it's almost clear now that there are, in fact, no SMP issues > with it (we don't do per-cluster locking, or anything ridiculous like > that), so unless Alfred has the reason again, I'll consider that method > again instead. Thanks for the constructive feedback. Yes it was NetBSD that did this. How do you plan on manipulating a linked list without switching from a simple atomic_int/dec to a complex global or hashed mutex operation? -- -Alfred Perlstein [alfred@freebsd.org] 'Instead of asking why a piece of software is using "1970s technology," start asking why software is ignoring 30 years of accumulated wisdom.' Tax deductible donations for FreeBSD: http://www.freebsdfoundation.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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