Date: Fri, 8 Dec 2000 14:04:54 -0800 From: Alfred Perlstein <bright@wintelcom.net> To: Terry Lambert <tlambert@primenet.com> Cc: Poul-Henning Kamp <phk@critter.freebsd.dk>, Chuck Paterson <cp@bsdi.com>, Mike Smith <msmith@FreeBSD.ORG>, smp@FreeBSD.ORG Subject: Re: Netgraph and SMP Message-ID: <20001208140454.S16205@fw.wintelcom.net> In-Reply-To: <200012082151.OAA24586@usr01.primenet.com>; from tlambert@primenet.com on Fri, Dec 08, 2000 at 09:51:41PM %2B0000 References: <80663.976310686@critter> <200012082151.OAA24586@usr01.primenet.com>
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* Terry Lambert <tlambert@primenet.com> [001208 13:52] wrote:
> > >For uses such as barriers for loading and unloading it is
> > >possible to have the counters and entry barriers all PCPU. You can then
> > >use more complex mechanisms to set the low level barrier and interrogate
> > >the counters. Terry ->>may<<- view this as another way of doing
> > >what he is suggesting.
> >
> > The thing that has me worried here is that using locking (as opposed
> > to atomic ops) in netgraph means that will expose netgraph paths to
> > heavy-duty locking synchronism, since TCP, UDP, IP, Mbuf will also
> > use a (separate) locking domain.
>
> It ought to reference on entry to netgraph; this will let it
> avoid locks for everything but adjusting the reference count,
> and won't damage reentrancy.
>
> It would mean stalling all of netgraph when loading or unloading
> a module, or establishing a connection or disconnecting nodes,
> though, but this might be OK.
>
> Sort of a BGL with multiple users/single manipulator for Netgraph.
>
>
> I think it's overly complicated, but you could also support the
> idea of per CPU connectedness, which would build the graph out
> on each CPU, making the relationship between nodes a per CPU
> thing. This would mean that you would not need to contend to
> build a graph per CPU, but that you would have to duplicate the
> build on each CPU. This would reduce to dealing with the lock
> only on load and unload (again). Each graph would need to set
> pointers to a shared state data object, though, since they are
> effectively the same objects with different function pointer
> linkages.
*hack* *hack* *hack* *hack* *hack* *hack* *hack* *hack*
(me not you. :))
netgraph_locks[NCPU];
netgraph_refs[NCPU];
unload() {
for (i = 0; i< NCPU; i++)
if (!mutex_try(&netgraph_locks[i]) {
i--;
goto error;
} else if (netgraph_refs[i] != 0) {
goto error;
}
do_unload();
return (0);
error:
while (i--)
mutex_unlock(&netgraph_locks[i])
return (EBUSY);
}
*hack* *hack* *hack* *hack* *hack* *hack* *hack* *hack*
?
--
-Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org]
"I have the heart of a child; I keep it in a jar on my desk."
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