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出没于杭州和青岛的程序猿一枚,对内核略懂一二

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分类: LINUX

2013-11-06 11:00:13

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Author: Tony

1.查看系统可用是时钟源

从代码来看,tsc的rating要大于hpet,的确是应该选择tsc的。那ULK3中提到的问题是怎么回事?

4. About tsc.
  TSC的性能要好于HPET:()
    TSC access is extremly fast as it is a per CPU register. HPET is a chipset device and scales bad when multiple CPUs try to access it simultanously as the access is serialized in hardware. Even on a UP system the access overhead is somewhere in the range of factor 100. 
  TSC主要有4种:
    Constant. Constant TSC means that the TSC does not change with CPU frequency changes, however it does change on C state transitions.
    Invariant. As described in the Intel manual: “The invariant TSC will run at a constant rate in all ACPI P-, C- and T-states”
    Non-stop. The Non-stop TSC has the properties of both Constant and Invariant TSC.
    None of the above. The TSC changes with the C, P and S state transitions
  并不是所有的TSC都可用:
    we only use the TSC, when: 
        - the TSC is known to be stable (not affected by CPU frequency changes) 
        - the TSC is sychronized accross CPUs 
    We also check the TSC with a watchdog mechanism, which verifies that is is keeping accurate time. When we detect that TSC does not, we replace it by the next available clock source.
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