Jörn Engel wrote:
Admitted, I'm a bit slow at times. But why does this matter?
According to my fairly limited brain, you take a potentially expensive
barrier, so you pay with a bit of runtime. What you buy is a smaller
critical section, so you can save some runtime on other cpus. When
optimizing for the common case, which is one cpu, this is a net loss.
There must be some correctness issue hidden that I cannot see. Can
you explain that to me?
Another CPU may find the bit clear, enter the critical section,
and load the old `likeliness_head' (value before being changed
by this CPU).
Then it stores the old value to likeliness->next, and overwrites
likeliness_head.
One CPU's update has now gotten lost.
(there are probably other examples, like missing likliness->type)
--
SUSE Labs, Novell Inc.
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