Re: spin_unlock optimization(i386)

Ingo Molnar (mingo@chiara.csoma.elte.hu)
Fri, 26 Nov 1999 20:21:11 +0100 (CET)

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> > if you want to trigger the bug, then you must _both_ read and write data
> > from one cpu. If one cpu writes data, and one cpu reads data, then
> > you'll never trigger the problem.
>
> yep, thats another type of causality violation, will try to generate a
> testcase. [i think i have one, i'm checking it now]

ok, the attached causal.c generates (the i believe simplest) such a
testcase. It's the basic causality test done on two CPUs, where both CPUs
are observers and 'creators' as well. Run it with:

./causal 0 2

to get the causality violation. [to speed up the triggering of a violation
on a >2CPU box, run it twice]

'./causal 1 2' does the stores via LOCK-ed instructions and i have not
managed to trigger the violation.

-- mingo

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