Rik van Riel <[email protected]> writes:
>
> If we always incremented the ticket number by 2 (instead of 1), then
> we could use the lower bit of the ticket number as the spinlock.
Spinning on a single bit is very inefficient, as you need to do
try lock in a loop which is very unfriendly to the MESI state protocol.
It's much better to have at least three states and allow
spinning-while-reading-only.
This is typically very visible on systems with >2S.
-Andi
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