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KVM: x86: Add module parameter for lapic periodic timer limit

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Certain guests, specifically RTOSes, request faster periodic timers than
what we allow by default. Add a module parameter to adjust the limit for
non-standard setups. Also add a rate-limited warning in case the guest
requested more.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Jan Kiszka 2011-09-12 14:10:22 +02:00 committed by Avi Kivity
parent bd80158aff
commit 9bc5791d4a
1 changed files with 13 additions and 2 deletions
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15
arch/x86/kvm/lapic.c
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@ -68,6 +68,9 @@
#define VEC_POS(v) ((v) & (32 - 1))
#define REG_POS(v) (((v) >> 5) << 4)
static unsigned int min_timer_period_us = 500;
module_param(min_timer_period_us, uint, S_IRUGO | S_IWUSR);
static inline u32 apic_get_reg(struct kvm_lapic *apic, int reg_off)
{
return *((u32 *) (apic->regs + reg_off));
@ -677,8 +680,16 @@ static void start_apic_timer(struct kvm_lapic *apic)
* scheduler.
*/
if (apic_lvtt_period(apic)) {
if (apic->lapic_timer.period < NSEC_PER_MSEC/2)
apic->lapic_timer.period = NSEC_PER_MSEC/2;
s64 min_period = min_timer_period_us * 1000LL;
if (apic->lapic_timer.period < min_period) {
pr_info_ratelimited(
"kvm: vcpu %i: requested %lld ns "
"lapic timer period limited to %lld ns\n",
apic->vcpu->vcpu_id, apic->lapic_timer.period,
min_period);
apic->lapic_timer.period = min_period;
}
}
hrtimer_start(&apic->lapic_timer.timer,