[cpp-threads] A niggle on the atomic model (N2145)

[Nick Maclaren]

Well, my copy of the Alpha architecture says at the end of 4-12:

    Although this is not recommended, the address specified by a STx_C
    instruction need not match that given by a preceding LDx_L.  Further,
    specifying unmatched addresses for those instructions requires an
    MB in between to guarantee ordering.

PLEASE specify that mapping the same physical location to two
virtual ones is undefined.  We may not see virtual caches or Alpha
style LDx_L/STx_C come back, but encouraging users to write code
that depends on them not doing so is asking for trouble.

Also, I would HATE to have to emulate a physical cache in software;
it might be possible, but I require notice of that question.


Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:  nmm1 at cam.ac.uk
Tel.:  +44 1223 334761    Fax:  +44 1223 334679