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    SubjectRe: [PATCH] sched: generalize CONFIG_IRQ_TIME_ACCOUNTING for X86 and ARM
    On 02/27/2012 02:12 PM, Peter Zijlstra wrote:

    >> -extern void enable_sched_clock_irqtime(void);
    >> -extern void disable_sched_clock_irqtime(void);
    >> +extern int sched_clock_irqtime;
    >> +static inline void enable_sched_clock_irqtime(void)
    >> +{
    >> + if (sched_clock_irqtime == -1)
    >> + sched_clock_irqtime = 1;
    >> +}
    >> +static inline void disable_sched_clock_irqtime(void)
    >> +{
    >> + sched_clock_irqtime = 0;
    >> +}
    >> #else
    >> static inline void enable_sched_clock_irqtime(void) {}
    >> static inline void disable_sched_clock_irqtime(void) {}
    >
    > Please keep them out-of-line, its not a fast path and it avoids having
    > to expose the state variable.

    OK

    >> +/*
    >> + * -1 if not initialized, 0 if disabled with "noirqtime" kernel option
    >> + * or after unstable clock was detected, 1 if enabled and active.
    >> + */
    >
    > You forgot to explain what you need the tri-state for.
    >
    >> +__read_mostly int sched_clock_irqtime = -1;

    The comment above should be a sufficient explanation, isn't it?

    It's a tri-state just because it "merges" two variables: internal state (enabled/disabled)
    and the value passed by "noirqtime" option (turn it on, default/turn it off). It can be
    enabled only if it was not turned off explicitly, i.e. -1 => 1 transition is possible,
    but 0 -> 1 is not. The same rule applies to a situation when an unstable clock is detected.

    Dmitry


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