On Sat, Aug 01, 2015 at 12:10:41PM +0200, Thomas Gleixner wrote:
> On Fri, 31 Jul 2015, Shaohua Li wrote:
> > @@ -336,6 +336,22 @@ static void __setup_APIC_LVTT(unsigned int clocks, int oneshot, int irqen)
> > apic_write(APIC_LVTT, lvtt_value);
> >
> > if (lvtt_value & APIC_LVT_TIMER_TSCDEADLINE) {
> > + u64 msr;
> > +
> > + /*
> > + * See Intel SDM: TSC-Deadline Mode chapter. In xAPIC mode,
> > + * writing APIC LVTT and TSC_DEADLINE MSR isn't serialized.
> > + * This uses the algorithm described in Intel SDM to serialize
> > + * the two writes
> > + * */
> > + while (1) {
> > + wrmsrl(MSR_IA32_TSC_DEADLINE, -1L);
> > + rdmsrl(MSR_IA32_TSC_DEADLINE, msr);
> > + if (msr)
> > + break;
> > + }
> > + wrmsrl(MSR_IA32_TSC_DEADLINE, 0);
>
>
> I think this is exceptionally silly. A proper fence after the
> apic_write() should have the same effect.
Not sure what happens in the hardware, I could have a try of fence, but
I'd prefer using the algorithm Intel described. This is not a fast path,
the loop will exit immediately regardless the issue occurs anyway.
Thanks,
Shaohua
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