Messages in this thread | | | Date | Fri, 26 Nov 2010 17:58:07 +0100 | From | Tejun Heo <> | Subject | Re: [thiscpuops upgrade 08/10] percpu: generic this_cpu_cmpxchg() and this_cpu_cmpxchg_double support |
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On 11/26/2010 05:56 PM, Eric Dumazet wrote: > Le vendredi 26 novembre 2010 à 17:51 +0100, Tejun Heo a écrit : >> On 11/24/2010 12:51 AM, Christoph Lameter wrote: >>> +/* >>> + * cmpxchg_double replaces two adjacent scalars at once. The first parameter >>> + * passed is a percpu pointer, not a scalar like the other this_cpu >>> + * operations. This is so because the function operates on two scalars >>> + * (must be of same size). A truth value is returned to indicate success or >>> + * failure (since a double register result is difficult to handle). >>> + * There is very limited hardware support for these operations. So only certain >>> + * sizes may work. >>> + */ >>> +#define __this_cpu_generic_cmpxchg_double(pcp, oval1, oval2, nval1, nval2) \ >> >> Ah... this is scary. If it proves to be useful enough, sure, but >> otherwise I'd like to avoid it. > > This is mandatory for several lockless algos, dont be afraid, its a > single instruction ;)
Thanks for holding my hands. :-)
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?
Thanks.
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