Hello!
Good turnout and some good questions here in Vancouver BC, please see
below for rough notes. ;-)
Thanx, Paul
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"Concurrency with tools/memory-model"
Andrea Parri presenting.
Rough notes of Q&A.
o Want atomic bit operation.
o But smp_read_barrier_depends() not there, so how to note pairing?
A: Note the dependency as the other end of the pairing.
o Speculation barriers, as in Spectre and Meltdown? A: This would
require adding timing, not in the immediate future.
o What ordering does system calls provide? A: None that we know of.
Boqun: Userspace needs to explicitly provide the needed ordering
when interacting with the kernel. Some architectures do provide
full barriers, but not to be counted on.
o Why herd7? A: Based on other formalizations -- note that herd7
had a number of hardware models. Paul: Plus the founder of the
LKMM project is a co-author of herd, which might have had some
effect.
o Why not also model interrupts and NMIs? Promela and spin have
been used for this. A: Cannot currently model them. You can
emulated them with additional threads and locks, if you wish.
Vincent Nimal and Lihao Liang have done some academic work on
these topics.
