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From: Aubrey Li <aubrey.intel@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: "Li, Aubrey" <aubrey.li@linux.intel.com>,
	"Lendacky, Thomas" <Thomas.Lendacky@amd.com>,
	Daniel Drake <drake@endlessm.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Linux Kernel <linux-kernel@vger.kernel.org>,
	Endless Linux Upstreaming Team <linux@endlessm.com>,
	Jiri Slaby <jslaby@suse.cz>
Subject: Re: [PATCH] x86/apic: Handle missing global clockevent gracefully
Date: Mon, 12 Aug 2019 20:59:42 +0800	[thread overview]
Message-ID: <CAERHkrttXdZhZHZs+JasZU6a2kEb1vc6KB25+LbpQycenJZpOg@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1908121423040.7324@nanos.tec.linutronix.de>

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

  reply	other threads:[~2019-08-12 12:59 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-01  6:24 setup_boot_APIC_clock() NULL dereference during early boot on reduced hardware platforms Daniel Drake
2019-08-01  7:16 ` Aubrey Li
2019-08-01  7:35   ` Thomas Gleixner
2019-08-01  7:56     ` Aubrey Li
2019-08-01  8:13       ` Thomas Gleixner
2019-08-01  8:21         ` Li, Aubrey
2019-08-01 10:13           ` Thomas Gleixner
2019-08-01 15:44             ` Lendacky, Thomas
2019-08-08 20:36               ` Thomas Gleixner
2019-08-08 21:01                 ` Lendacky, Thomas
2019-08-08 21:08                   ` Thomas Gleixner
2019-08-08 21:36                     ` Lendacky, Thomas
2019-08-09 12:54                       ` [PATCH] x86/apic: Handle missing global clockevent gracefully Thomas Gleixner
2019-08-09 12:59                         ` Jiri Slaby
2019-08-09 13:58                         ` Lendacky, Thomas
2019-08-09 19:40                           ` Thomas Gleixner
2019-08-12  6:16                         ` Daniel Drake
2019-08-12  7:03                           ` Jiri Slaby
2019-08-15  5:02                           ` Daniel Drake
2019-08-12  7:46                         ` Li, Aubrey
2019-08-12 12:24                           ` Thomas Gleixner
2019-08-12 12:59                             ` Aubrey Li [this message]
2019-08-12 17:11                               ` Thomas Gleixner
2019-08-19 10:37                         ` [tip:x86/urgent] " tip-bot for Thomas Gleixner
2019-08-01  9:00   ` setup_boot_APIC_clock() NULL dereference during early boot on reduced hardware platforms Daniel Drake
2019-08-01 10:17     ` Thomas Gleixner
2019-08-01  7:27 ` Thomas Gleixner

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