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SubjectRe: [PATCH] x86/apic: Handle missing global clockevent gracefully
On Mon, Aug 12, 2019 at 8:25 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> On Mon, 12 Aug 2019, Li, Aubrey wrote:
> > On 2019/8/9 20:54, 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) {
> >
> > Is this loop still meaningful, can we just invoke the handler twice
> > before and after the tick?
>
> And that solves what?
>

I meant, can we do this one time?
- lapic_cal_t1 = read APIC counter
- /* Wait for a tick to elapse */
- lapic_cal_t2 = read APIC counter

I'm not clear why we still need this loop, to use the
existing lapic_cal_handler()?

Thanks,
-Aubrey

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