On 08/27/2011 06:07 PM, Mathieu Desnoyers wrote:
Update nto1 selective model
The nto1 selective wakeup model introduced by Paolo was:
a) too complex (tried to model the full-blown RCU rather than a simple
queue system)
b) did not model progress with wakers running for a limited amount of
iterations, only with wakers running infinitely often (which
therefore does not prove anything).
What we really want to model here is what happens if we have wakers
running a few times, and then not running for a very long time: can we
end up with a missed wakeup, and therefore end up with an enqueued entry
but with the waiter waiting forever ?
See
http://git.lttng.org/?p=userspace-rcu.git;a=blob;f=futex-wakeup/nto1-selective/futex.spin;h=6f854fceefba73dfbc3781d04734b75590175159;hb=refs/heads/formal-model
Thanks!
Makes sense regarding the complexity.
Regarding (b), I am not sure I understand. It is true that wakers run
infinitely often, but they do nothing until all of them have progressed.
Also, since the queue state is binary, Spin should exhaust its state
space without running wakers more than twice; it should be possible to
add an assertion about this.
I think we are simply testing different things. Perhaps we want to keep
both models?
Paolo
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