Chris Wright wrote:
Thanks for the review! Comments inline.
>> +/* paravirt_ops.get_wallclock = vmi_get_wallclock */
>>
>
> Style nit, these pv_ops.foo = vmi_foo style comments aren't really useful.
>
>
Yeah, and easy to get out of sync. I'll drop them.
>> + .rating = 1000,
>>
>
> Heh, no messing around ;-)
>
Yes, VMI has 1000 hps.
>> + printk(KERN_WARNING "vmi: registering clock event %s. mult=%lu shift=%u\n",
>> + evt->name, evt->mult, evt->shift);
>>
>
> Why is this a warning? ;-)
>
Debug info, I can remove it.
>> +void __init vmi_time_init(void)
>> +{
>> + /* Disable PIT: BIOSes start PIT CH0 with 18.2hz peridic. */
>> + outb_p(0x3a, PIT_MODE); /* binary, mode 5, LSB/MSB, ch 0 */
>>
>
> That shouldn't be necessary using clockevents.
>
Actually, I'm not so sure. If clockevents simply masks the PIT when
disabling it, we still have overhead of keeping the latch in sync, which
requires a timer at the PIT frequency. I can instrument to see how
exactly the PIT gets disabled.
>> + vmi_time_init_clockevent();
>> + setup_irq(0, &vmi_clock_action);
>> +}
>> +
>> +#ifdef CONFIG_X86_LOCAL_APIC
>> +void __devinit vmi_time_bsp_init(void)
>> +{
>> + /*
>> + * On APIC systems, we want local timers to fire on each cpu. We do
>> + * this by programming LVTT to deliver timer events to the IRQ handler
>> + * for IRQ-0, since we can't re-use the APIC local timer handler
>> + * without interfering with that code.
>> + */
>> + clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
>>
>
> Why do you do this suspend...
>
We need to cancel all pending PIT timer events and restart then local
timer, which requires atomically taking over IRQ-0. We use the IDT gate
for IRQ-0 because it is already an exclusive interrupt, but we can't
re-use the LVTT IDT gate for local timer since that requires a custom
custom SMP interrupt in entry.S. So we must be absolutely sure when we
get an interrupt on IRQ-0 that it came from the VMI local (rather than
PIT) delivery path.
>
>> + local_irq_disable();
>> +#ifdef CONFIG_X86_SMP
>> + /*
>> + * XXX handle_percpu_irq only defined for SMP; we need to switch over
>> + * to using it, since this is a local interrupt, which each CPU must
>> + * handle individually without locking out or dropping simultaneous
>> + * local timers on other CPUs. We also don't want to trigger the
>> + * quirk workaround code for interrupts which gets invoked from
>> + * handle_percpu_irq via eoi, so we use our own IRQ chip.
>> + */
>> + set_irq_chip_and_handler_name(0, &vmi_chip, handle_percpu_irq, "lvtt");
>> +#else
>> + set_irq_chip_and_handler_name(0, &vmi_chip, handle_edge_irq, "lvtt");
>> +#endif
>> + vmi_wiring = VMI_ALARM_WIRED_LVTT;
>> + apic_write(APIC_LVTT, vmi_get_timer_vector());
>>
>
> isn't this just your ->startup?
>
Which structure has a ->startup function we can use? Sorry if this
seems ignorant, I'm not quite sure what you mean.
>
>> + local_irq_enable();
>> + clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);
>>
>
> ...and resume? Instead of letting clockevents core handle all of that,
> and just registering right here?
>
It wasn't clear that clockevents would issue a resume notify for us; if
so we could handle this setup in the callback, but it has to be done on
the correct CPU. I can try it and see if that works.
Thanks,
Zach
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