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POHow do the likely() and unlikely() macros in the Linux kernel work and what is their benefit?
 

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    1. USCiro Santilli 新疆改造中心 六四事件 法轮功
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    1. COThis really isn't specific to the Linux kernel or about macros, but a compiler optimization. Should this be retagged to reflect that?
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      1. POHow do the likely() and unlikely() macros in the Linux kernel work and what is their benefit?
      1. USCody Brocious
    2. COThe paper [What every Programmer should know about Memory](http://people.redhat.com/drepper/cpumemory.pdf) (p. 57) contains an in-depth explanation.
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      1. POHow do the likely() and unlikely() macros in the Linux kernel work and what is their benefit?
      1. USTorsten Marek
    3. COAccording to the [kernelnewbies FAQ](http://kernelnewbies.org/FAQ/LikelyUnlikely) (and the latest 3.11 kernel source), the macros definitions are slightly different now: #define likely(x) __builtin_expect(!!(x), 1) #define unlikely(x) __builtin_expect(!!(x), 0) I guess this adds a little more to the confusion!? :) I don't get the need for double NOT (<code>!!</code>).
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      1. POHow do the likely() and unlikely() macros in the Linux kernel work and what is their benefit?
      1. USMandeep Sandhu
 

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