I noticed today that the ARC statistics are maintained with atomic operations.
(This is even called out in a comment, so it?s not a great insight.)
This seems like a potential scalability problem on multi-CPU systems. The cache
line involved is going to bounce back and forth at a fairly high rate.
These statistics should probably be kept on a per-CPU basis. (Nothing actually
reads them right now, so the cost of aggregation is 0 at present. ;-)
Switching to non-atomic operations doesn''t buy a whole lot since the
writes will force cache line exclusivity anyway.
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