Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [thiscpuops upgrade 08/10] percpu: generic this_cpu_cmpxchg() and this_cpu_cmpxchg_double support | From | Eric Dumazet <> | Date | Fri, 26 Nov 2010 18:16:16 +0100 |
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Le vendredi 26 novembre 2010 à 18:07 +0100, Tejun Heo a écrit : > On 11/26/2010 06:01 PM, Eric Dumazet wrote: > >> What I'm afraid of is generic code switching to use it in very hot > >> paths when a lot of archs can't actually do it leading to performance > >> regressions. Is this something which is available on most archs? > >> > > > > I would say cmpxchg() has the same problem, some arches dont have a > > native instruction, yet we use it in some paths. > > Yeah, well, there's difference between some not having it and only > x86_64 having it. cmpxchg was already rather well received when it > was added even though it wasn't available on all archs. I'm not > against it but think we should use some caution here and think about > the impact of unoptimized cases which can be pretty common (preemption > toggling isn't too expensive but irq toggling can be quite). >
x86_32 has it too
x86_64 uses cmpxchg16b, while x86_32 uses cmpxhg8b
And I guess it will be used in contexts we had to disable irqs, so it will be faster on x86, and same cost on other arches.
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