Re: [PATCH] x86/apic: Handle missing global clockevent gracefully

[Thomas Gleixner]

On Fri, 9 Aug 2019, Lendacky, Thomas wrote:
> On 8/9/19 7:54 AM, Thomas Gleixner wrote:
> > +	local_irq_disable();
> >   	/*
> >   	 * Setup the APIC counter to maximum. There is no way the lapic
> >   	 * can underflow in the 100ms detection time frame
> >   	 */
> >   	__setup_APIC_LVTT(0xffffffff, 0, 0);
> >   
> > -	/* Let the interrupts run */
> > -	local_irq_enable();
> > +	/*
> > +	 * Methods to terminate the calibration loop:
> > +	 *  1) Global clockevent if available (jiffies)
> > +	 *  2) TSC if available and frequency is known
> > +	 */
> > +	jif_start = READ_ONCE(jiffies);
> > +
> > +	if (tsc_khz) {
> > +		tsc_start = rdtsc();
> > +		tsc_perj = div_u64((u64)tsc_khz * 1000, HZ);
> > +	}
> > +
> > +	while (lapic_cal_loops <= LAPIC_CAL_LOOPS) {
> > +		/*
> > +		 * Enable interrupts so the tick can fire, if a global
> > +		 * clockevent device is available
> > +		 */
> > +		local_irq_enable();
> 
> Just a nit, but you end up doing this at the bottom of the loop, so you
> could move this invocation to just before the loop and avoid doing two
> local_irq_enable() calls in succession after the first iteration.

Indeed. Lets see how the reports go. That change is a nobrainer.

Thanks,

	tglx