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    SubjectRe: [PATCH 10/17] 2.6.17.1 perfmon2 patch for review: PMU context switch
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    > So why do we need care about context switch in cpu-wide mode?
    > It is because we support a mode where the idle thread is excluded
    > from cpu-wide monitoring. This is very useful to distinguish
    > 'useful kernel work' from 'idle'.

    I don't quite see the point because on x86 the PMU doesn't run
    during C states anyways. So you get idle excluded automatically.

    And on the other hand a lot of people especially want idle
    accounting too and boot with idle=poll. Your explicit
    code would likely defeat that.

    > As you realize, that means
    > that we need to turn off when the idle thread is context switched
    > in and turn it back on when it is switched off.

    Also x86-64 has idle notifiers for this if you really wanted
    to do it properly.

    -Andi
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