prevalent如何目前CPU的分支prediction？ [英] How prevalent is branch prediction on current CPUs?
问题描述
由于对性能的影响巨大，我从来不知道我现在的天台式机的CPU均设有分公司prediction。当然有。但如何对各种ARM的产品？难道iPhone或Android手机有分支prediction？旧的任天堂的DS？如何基于PowerPC的Wii？ PS 3？
Due to the huge impact on performance, I never wonder if my current day desktop CPU has branch prediction. Of course it does. But how about the various ARM offerings? Does iPhone or android phones have branch prediction? The older Nintendo DS? How about PowerPC based Wii? PS 3?
他们是否有一个复杂的prediction单位不是那么重要，但如果他们至少的部分的动态prediction，以及他们是否做的部分的以下预期的分支指令的执行。
Whether they have a complex prediction unit is not so important, but if they have at least some dynamic prediction, and whether they do some execution of instructions following an expected branch.
什么是与分支prediction的CPU截止？几十年来，从一个手持计算器前显然没有之一，而我的桌面一样。但是，任何人都可以更清晰地勾勒出其中一个可以预期的动态分支prediction？
What is the cutoff for CPUs with branch prediction? A hand held calculator from decades ago obviously doesn't have one, while my desktop does. But can anyone more clearly outline where one can expect dynamic branch prediction?
如果还不清楚，我说的那种prediction那里的情况正在发生变化，在运行时改变预期的路径。
If it is unclear, I am talking about the kind of prediction where the condition is changing, varying the expected path during runtime.
推荐答案
长管线现代高端超标量处理器（这意味着几乎所有CPU的台式机和服务器中常见的）有相当精密复杂的分支prediction这些天。
Modern high end superscalar CPUs with long pipelines (which means almost all CPUs commonly found in desktops and servers) have quite sophisticated branch prediction these days.
大多数的ARM CPU不具有分支prediction，从而节省硅和功耗，但的ARM CPU一般都相对较短的管道。也为在ARM最指令的条件执行的支持ISA有助于减少所需的分支数（因而减轻了分支误prediction摊位的费用）。
Most ARM CPUs do not have branch prediction, which saves silicon and power consumption, but ARM CPUs generally have relatively short pipelines. Also the support for conditional execution of most instructions in the ARM ISA helps to reduce the number of branches required (and hence mitigates the cost of branch misprediction stalls).
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