Re: MP locking?

[buhrow%lothlorien.nfbcal.org@localhost (Brian Buhrow)]

        Hello.  Having just recently spent quite a bit of time porting a kernel
module from NetBSD-3 to NetBSD-5, and working out a bunch of
synchronization issues, I suggest skipping over NetBSD-4 and going straight
for 5.  You'll get better multi-cpu capability, and it looks like the
locking APIs in 5.x will be longer lived going forward than the now
depracated and no longer functioning APIs in 4.x and earlier.
-Brian

On Jul 1, 11:13am, Manuel Bouyer wrote:
} Subject: Re: MP locking?
} On Wed, Jun 30, 2010 at 05:15:53PM -0400, der Mouse wrote:
} > I have some kernel code which was written for a pre-MP kernel; it uses
} > spl*() for locking.
} > I'd like to roll this forward to something at
} > least slightly more modern - specifically, a dual-CPU 4.0.1 machine.
} > 
} > lock(9) outlines locking facilities which I believe I can use to do
} > what I want - but there are other issues, such as cache coherency; do I
} > need to do anything special with shared data structures to ensure
} > coherency between processors?  Is it enough to declare them volatile,
} > or do I need memory barriers as well, or what?
} 
} You need memory barriers, modern CPUs can do speculative reads, and some
} can reorder writes. AFAIK, lock operations act as memory barriers.
} atomic ops do not.
} 
} -- 
} Manuel Bouyer <bouyer%antioche.eu.org@localhost>
}      NetBSD: 26 ans d'experience feront toujours la difference
} --
>-- End of excerpt from Manuel Bouyer