On Thu, 6 Oct 2005, Andrey Savochkin wrote:
>
> I start to wonder about existing mainstream code, presumably bug-free, that
> uses spinlocks without any problematic restart.
Actually, a number of cases where we found things to be a problem have
been converted.
It _is_ a real-life issue, although with "normal" code it only happens in
extreme machines (NUMA with tons of nodes). It's fairly fundamental in
NUMA, and in many ways you do absolutely _not_ want fairness, because it's
much better to take the lock locally a hundred times (almost free) than it
is to bounce it back-and-forth between two nodes a hundred times (very
expensive).
Fairness is often very expensive indeed.
But places where unfairness can be a problem have been converted to things
like RCU, which allows concurrent operations more gracefully.
And sometimes the answer is just "don't do that then".
Linus
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