On 09/05/2015 15:28, Konstantin Belousov wrote:
> +void
> +acpi_cpu_idle_mwait(uint32_t mwait_hint)
> +{
> + int *state;
> +
> + state = (int *)PCPU_PTR(monitorbuf);
> + /*
> + * XXXKIB. Software coordination mode should be supported,
> + * but all Intel CPUs provide hardware coordination.
> + */
> + cpu_monitor(state, 0, 0);
> + cpu_mwait(MWAIT_INTRBREAK, mwait_hint);
> +}
> +
Kostik,
it's been a while since I studied this code, so please pardon me if I am asking
something obvious or silly.
I wonder why this function does not set 'state' before monitor + mwait.
As far as I can see, all other idling functions do that. And cpu_idle_wakeup()
compares the state to STATE_MWAIT before changing it.
So, I am concerned that if the state happens to be anything other than
STATE_MWAIT when acpi_cpu_idle_mwait() is called, then cpu_idle_wakeup() won't
wake up the idled CPU. It seems that if the state is not STATE_SLEEPING then an
IPI won't be sent either. Actually, that leaves STATE_RUNNING is the only
problematic case, but that's probably the state that the CPU would have before
idling.
--
Andriy Gapon
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