Messages in this thread Patch in this message | | | Subject | Why we need to call cpu_idle() with preemption disabled | From | Wu Zhangjin <> | Date | Tue, 16 Mar 2010 17:01:54 +0800 |
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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 enabled?
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) */ init_idle_bootup_task(current); preempt_enable_and_schedule(); - preempt_disable(); - /* Call into cpu_idle with preempt disabled */ + /* There is no reason for calling cpu_idle with preemption disabled */ cpu_idle(); }
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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