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    SubjectRe: [PATCH 3/3] trace points: power: remove 'cpu_id' from trace_cpu_idle

    2011/8/20 Thomas Renninger <>:
    > On Friday, August 19, 2011 05:04:04 PM wrote:
    >> From: Ming Lei <>
    >> This patch removes the 'cpu_id' parameter of the cpu_idle
    >> trace point, based on the ideas below:
    >> - the cpu_id which is passed to trace point is always the current
    >>   cpu
    > Are you sure this will always be true?

    It is sure at least now, the only place to pass 'dev->cpu' is inside
    but the cpuidle_device is got from __this_cpu_read(cpuidle_devices),
    so it should
    be true for such case.

    >> - the current cpu info has been included into the trace result
    >>   already
    >> - smp_processor_id() can't be used safely in preemptible context.
    > The cpuid has been added to idle events on purpose for example to be
    > able to pass C-state dependencies.
    > 2 cores may only enter a deeper sleep state if the 2nd core enters it
    > as well.
    > There may be architectures where you could trigger a sleep state on
    > a foreign cpu.
    > This may not be used now, but if the kernel does want to use it, you do
    > not want to adjust a dozen userspace apps.
    > Not sure how to quickly solve the:
    > "smp_processor_id() can't be used safely in preemptible context."
    > problem, though.
    > A convention could be declared that if -1 is passed, it's the same cpu
    > entering the sleep state as the running one. This will probably
    > break userspace apps as well...
    > Best would be to clean up x86 and let idle routines always be entered
    > from cpuidle subsystem which knows the cpu id already and eliminate
    > all idle functions in arch/x86/kernel/process.c.
    >   Thomas
    > PS: I do not care about patch 1 and 2 as these events are ARM specific
    > afaik. But I vote against this one.

    Ming Lei
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