Re: [PATCH gnumach] lapic timer: Calibrate based on 10 PIT sleeps for 10ms

[Samuel Thibault]

Applied, thanks!

Damien Zammit, le dim. 26 févr. 2023 01:31:18 +0000, a ecrit:
> NB: This relies on a fix for QEMU as one-shot PIT mode
> is currently broken in qemu.
> ---
>  i386/i386at/ioapic.c | 19 +++++++++++--------
>  1 file changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/i386/i386at/ioapic.c b/i386/i386at/ioapic.c
> index 24e04653..d2ea84ad 100644
> --- a/i386/i386at/ioapic.c
> +++ b/i386/i386at/ioapic.c
> @@ -151,8 +151,9 @@ ioapic_toggle_entry(int apic, int pin, int mask)
>  }
> 
>  static uint32_t
> -pit_measure_apic_hz(void)
> +pit_measure_10x_apic_hz(void)
>  {
> +    volatile int i;
>      uint32_t start = 0xffffffff;
> 
>      /* Prepare accurate delay for 1/hz seconds */
> @@ -162,7 +163,8 @@ pit_measure_apic_hz(void)
>      lapic->init_count.r = start;
> 
>      /* zZz */
> -    pit_sleep();
> +    for (i = 0; i < 10; i++)
> +        pit_sleep();
> 
>      /* Stop APIC timer */
>      lapic->lvt_timer.r |= LAPIC_DISABLE;
> @@ -181,13 +183,13 @@ lapic_enable_timer(void)
>  {
>      /* Set up counter */
>      lapic->init_count.r = calibrated_ticks;
> -    lapic->divider_config.r = LAPIC_TIMER_DIVIDE_16;
> +    lapic->divider_config.r = LAPIC_TIMER_DIVIDE_2;
> 
>      /* Set the timer to interrupt periodically on remapped timer GSI */
>      lapic->lvt_timer.r = IOAPIC_INT_BASE | LAPIC_TIMER_PERIODIC;
> 
>      /* Some buggy hardware requires this set again */
> -    lapic->divider_config.r = LAPIC_TIMER_DIVIDE_16;
> +    lapic->divider_config.r = LAPIC_TIMER_DIVIDE_2;
> 
>      /* Enable interrupts for the first time */
>      printf("LAPIC timer configured on cpu%d\n", cpu_number());
> @@ -336,12 +338,13 @@ ioapic_configure(void)
>      lapic_enable();
> 
>      /* Set one-shot timer */
> -    lapic->divider_config.r = LAPIC_TIMER_DIVIDE_16;
> +    lapic->divider_config.r = LAPIC_TIMER_DIVIDE_2;
>      lapic->lvt_timer.r = IOAPIC_INT_BASE;
> 
> -    /* Measure number of APIC timer ticks in 1/hz seconds
> -     * but calibrate the timer to expire at rate of hz */
> -    calibrated_ticks = pit_measure_apic_hz() * hz;
> +    /* Measure number of APIC timer ticks in 10x 1/hz seconds
> +     * but calibrate the timer to expire at rate of hz
> +     * divide by 10 because we waited 10 times longer than we needed */
> +    calibrated_ticks = pit_measure_10x_apic_hz() / 10;
> 
>      /* Set up counter later */
>      lapic->lvt_timer.r = LAPIC_DISABLE;
> --
> 2.39.0
> 
> 
> 

-- 
Samuel
---
Pour une évaluation indépendante, transparente et rigoureuse !
Je soutiens la Commission d'Évaluation de l'Inria.