Re: [PATCH v5 08/12] x86/ioapic: Refactor the delay logic in timer_irq_works()

[Dou Liyang]

Hi Thomas,

At 07/03/2017 03:15 AM, Thomas Gleixner wrote:
> On Fri, 30 Jun 2017, Dou Liyang wrote:
> > +static void __init delay_with_tsc(void)
> > +{
> > +	unsigned long long start, now;
> > +	unsigned long ticks = jiffies;
>
> Please make that
>
>        unsigned long end = jiffies + 4;
>
> ticks really means: number of ticks. But that variable is doing something
> different.

um, I see. Will use 'end' instead.

> > +	start = rdtsc();
> > +
> > +	/*
> > +	 * We don't know the TSC frequency yet, but waiting for
> > +	 * 40000000000/HZ TSC cycles is safe:
> > +	 * 4 GHz == 10 jiffies
> > +	 * 1 GHz == 40 jiffies
> > +	 */
> > +	do {
> > +		rep_nop();
> > +		now = rdtsc();
> > +	} while ((now - start) < 40000000000UL / HZ &&
> > +		time_before_eq(jiffies, ticks + 4));
> > +}
> > +
> > +static void __init delay_without_tsc(void)
> > +{
> > +	int band = 1;
> > +	unsigned long ticks = jiffies;
>
> Please sort variables in reverse fir tree order
>
> 	unsigned long end = jiffies + 4;
> 	int band = 1;

OK, I will.

> > +
> > +	/*
> > +	 * We don't know any frequency yet, but waiting for
> > +	 * 40940000000/HZ cycles is safe:
> > +	 * 4 GHz == 10 jiffies
> > +	 * 1 GHz == 40 jiffies
> > +	 * 1 << 1 + 1 << 2 +...+ 1 << 11 = 4094
> > +	 */
> > +	do {
> > +		__delay(((1 << band++) * 10000000UL) / HZ);
>
>   s/1/1U/

Got it!

Thanks,

	dou.


> > +	} while (band < 12 && time_before_eq(jiffies, ticks + 4));
> > +}
>
> Thanks,
>
> 	tglx