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SubjectRe: [PATCH v7] KVM: LAPIC: Apply change to TDCR right away to the timer
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On 06/10/2017 16:01, Wanpeng Li wrote:
> + if (!apic->lapic_timer.period)
> + return;
> +
> + now = ktime_get();
> + remaining = ktime_sub(apic->lapic_timer.target_expiration, now);
> + if (ktime_to_ns(remaining) < 0)
> + remaining = 0;
> + delta = mod_64(ktime_to_ns(remaining), apic->lapic_timer.period);

I think this shouldn't be happening. If it does, I'm not sure the mod
is the right thing to do, so I'd just use ktime_to_ns(remaining).

So perhaps let's simplify all this to:

ns_remaining_old = ktime_to_ns(remaining);
ns_remaining_new = mul_u64_u32_div(ns_remaining_old,
apic->divide_count, old_divisor);

because below you're calling nsec_to_cycles but remaining is not expressed
in nanoseconds.

> + if (!delta)
> + return;
> +
> + delta = delta * apic->divide_count / old_divisor;
> +
> + limit_periodic_timer_frequency(apic);

This should be done before all the "if"s (which should not be there in v8,
but you should still call it before "now = ktime_get();").

Paolo

> + apic->lapic_timer.tscdeadline += nsec_to_cycles(apic->vcpu, delta) -
> + nsec_to_cycles(apic->vcpu, remaining);
> + apic->lapic_timer.target_expiration = ktime_add_ns(now, delta);
> +}

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