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    SubjectWhy we need to call cpu_idle() with preemption disabled
    Hi, Thomas

    Just traced the preemption latency of 2.6.33-rt7 on my Yeeloong netbook
    with the preemptoff tracer of Ftrace and found it is very big in
    cpu_idle(), more than 1000 us.

    And found that we have called cpu_idle() in init/main.c with preemption
    disabled? why we need to do it? can we simply call it with preemption

    diff --git a/init/main.c b/init/main.c
    index 48393c0..437ac34 100644
    --- a/init/main.c
    +++ b/init/main.c
    @@ -428,9 +428,8 @@ static noinline void __init_refok rest_init(void)
    - preempt_disable();

    - /* Call into cpu_idle with preempt disabled */
    + /* There is no reason for calling cpu_idle with preemption
    disabled */

    After removing that preempt_disable() and the related operations around
    the calling to __schedule() in the cpu_idle(), the result becomes around
    200 us, which is acceptable for I have enabled several Ftrace tracers.
    Best Regards,
    Wu Zhangjin

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      Last update: 2010-03-16 10:11    [W:0.021 / U:6.160 seconds]
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