On Thu, 1 Nov 2007, Gregory Haskins wrote:
>
> I had observed this phenomenon on some 8-ways here as well, but I didn't
> have the bandwidth to code something up. Thumbs up!
Can you test under interesting loads?
We're interested in:
- is the unfairness fix really noticeable (or does it just move the
problem somewhere else, and there is no real change in behaviour)
- what is the performance impact?
In particular, unfair spinlocks have the potential to perform much better.
Not so much because the spinlock itself acts all that differently, but
because being unfair also fundmanetally tends to keep the data structures
that are *protected* by the spinlock on just one CPU.
So "unfair" is obviously always bad. Except when it isn't. I'd personally
like to merge the ticket spinlocks, but I'd really like to have people who
have real loads where they matter actually also do some performance
testing. Because I do think it will potentially be a performance downer.
(I obviously hope it won't be, but..)
Linus
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