Re: [patch, 2.6.10-rc2] sched: fix ->nr_uninterruptible handlingbugs

[Paul Jackson]

A long time ago, Linus wrote:
> An atomic op is pretty much as expensive as a spinlock/unlock pair on x86.  
> Not _quite_, but it's pretty close.

Are both read and modify atomic ops relatively expensive on some CPUs,
or is it just modify atomic ops?

(Ignoring for this question the possibility that a mix of read and
modify ops could heat up a cache line on multiprocessor systems, and
focusing for the moment just on the CPU internals ...)

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@xxxxxxx> 1.650.933.1373, 1.925.600.0401
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