I have now found an implementation using LL/SC for the PPC in the
Darwin
kernel, however what disconcerts me is the fact that the erronous CAS
based solution is still part of the kernel source(!), and that
AFAIK x86
I wouldn't call it "erronous", it is just that it assumes that certain
protocol guaranteeing that no ABA ever happens is followed by its
clients.
does not have LL/SC instructions [and a whole bunch of other read-
modify-
write instructions can be made atomic with a lock prefix] - I
posted a bug
LL/SC cannot be emulated through x86 lock prefix, if that's what you
are
talking about.
I'd say:
(1) IMO, it's a bug; thanks for filing the bug report, Colin; do you
have the # handy? I'd like to look at it...
(2) You can implement LL/SC from either RLL/RSC or CAS primitives:
Efficient and practical constructions of LL/SC variables
Annual ACM Symposium on Principles of Distributed Computing
Proceedings of the twenty-second annual symposium on Principles
of distributed computing
Prasad Jayanti, Srdjan Petrovic - Dartmouth College Hanover, NH
You can access the paper through the ACM portal, or from www.cs.dartmouth.edu/~spetrovic/papers/podc_LLSC.pdf
There's also a 2004 IBM research report on using CAS at www.research.ibm.com/people/m/michael/RC23220.pdf
-- Terry
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