svn commit: r282678 - in head: share/man/man4 sys/amd64/acpica sys/amd64/include sys/dev/acpica sys/i386/acpica sys/i386/include sys/x86/include sys/x86/x86

Andriy Gapon avg at FreeBSD.org
Mon May 18 11:30:54 UTC 2015


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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