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

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

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.

> +     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;

> +
> +     /*
> +      * 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/

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

Thanks,

        tglx

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