Subject: Re: SMP re-entrancy in kernel drivers/"bottom half?"
To: Jonathan Stone <>
From: Daniel Carosone <>
List: tech-kern
Date: 12/18/2003 13:10:53
> Hm. Data structures outside such SMP-save drivers still need a
> (`global', in your term) spinlock corresponding to IPL_NET or IP_BIO.

Which the smp-safe driver will have to aquire (via traditional splX?)
before maniupulating. mbuf chains seem the logical example.

If they don't do this, they're probably not very interesting
drivers. :-)

> When I think of a machine with a half-dozen gigabit nics, or (very
> soon) a couple of ten-gigabit NICs, this sounds like a very useful
> halfway house between a single-big-lock kernel and real fine-grained
> SMP locking.

It certainly sounds like a reasonable compromise, but whether its
useful or not will need to be measured (ie, do they spend most of
their time holding the global locks on mbufs anyway).

Fortunately, it sounds like implementing it for the purposes of the
experiment should be relatively easy.