Re: [PATCH] sched: generalize CONFIG_IRQ_TIME_ACCOUNTING for X86and ARM

[Dmitry Antipov]

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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