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

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Date:   Mon, 12 Aug 2019 14:24:25 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Li, Aubrey" <aubrey.li@...ux.intel.com>
cc:     "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        Daniel Drake <drake@...lessm.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Endless Linux Upstreaming Team <linux@...lessm.com>,
        Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH] x86/apic: Handle missing global clockevent gracefully

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?

> Thanks,
> -Aubrey

<Remove tons of useless quote>

Can you please trim your replies?

Thanks,

	tglx