From d24c954fa7a252b093fa8ba9ed12c00bc3829bbe Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Wed, 8 Apr 2015 20:33:25 -0300 Subject: [PATCH 2/2] KVM: lapic: mark LAPIC timer handler as irqsafe Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.0/patches-4.0.8-rt6.tar.xz Since lapic timer handler only wakes up a simple waitqueue, it can be executed from hardirq context. Also handle the case where hrtimer_start_expires fails due to -ETIME, by injecting the interrupt to the guest immediately. Reduces average cyclictest latency by 3us. Signed-off-by: Marcelo Tosatti Signed-off-by: Sebastian Andrzej Siewior --- arch/x86/kvm/lapic.c | 40 +++++++++++++++++++++++++++++++++++++--- 1 file changed, 37 insertions(+), 3 deletions(-) --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1130,8 +1130,36 @@ void wait_lapic_expire(struct kvm_vcpu * __delay(tsc_deadline - guest_tsc); } +static enum hrtimer_restart apic_timer_fn(struct hrtimer *data); + +static void __apic_timer_expired(struct hrtimer *data) +{ + int ret, i = 0; + enum hrtimer_restart r; + struct kvm_timer *ktimer = container_of(data, struct kvm_timer, timer); + + r = apic_timer_fn(data); + + if (r == HRTIMER_RESTART) { + do { + ret = hrtimer_start_expires(data, HRTIMER_MODE_ABS); + if (ret == -ETIME) + hrtimer_add_expires_ns(&ktimer->timer, + ktimer->period); + i++; + } while (ret == -ETIME && i < 10); + + if (ret == -ETIME) { + printk_once(KERN_ERR "%s: failed to reprogram timer\n", + __func__); + WARN_ON_ONCE(1); + } + } +} + static void start_apic_timer(struct kvm_lapic *apic) { + int ret; ktime_t now; atomic_set(&apic->lapic_timer.pending, 0); @@ -1162,9 +1190,11 @@ static void start_apic_timer(struct kvm_ } } - hrtimer_start(&apic->lapic_timer.timer, + ret = hrtimer_start(&apic->lapic_timer.timer, ktime_add_ns(now, apic->lapic_timer.period), HRTIMER_MODE_ABS); + if (ret == -ETIME) + __apic_timer_expired(&apic->lapic_timer.timer); apic_debug("%s: bus cycle is %" PRId64 "ns, now 0x%016" PRIx64 ", " @@ -1196,8 +1226,10 @@ static void start_apic_timer(struct kvm_ do_div(ns, this_tsc_khz); expire = ktime_add_ns(now, ns); expire = ktime_sub_ns(expire, lapic_timer_advance_ns); - hrtimer_start(&apic->lapic_timer.timer, + ret = hrtimer_start(&apic->lapic_timer.timer, expire, HRTIMER_MODE_ABS); + if (ret == -ETIME) + __apic_timer_expired(&apic->lapic_timer.timer); } else apic_timer_expired(apic); @@ -1678,6 +1710,7 @@ int kvm_create_lapic(struct kvm_vcpu *vc hrtimer_init(&apic->lapic_timer.timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); apic->lapic_timer.timer.function = apic_timer_fn; + apic->lapic_timer.timer.irqsafe = 1; /* * APIC is created enabled. This will prevent kvm_lapic_set_base from @@ -1803,7 +1836,8 @@ void __kvm_migrate_apic_timer(struct kvm timer = &vcpu->arch.apic->lapic_timer.timer; if (hrtimer_cancel(timer)) - hrtimer_start_expires(timer, HRTIMER_MODE_ABS); + if (hrtimer_start_expires(timer, HRTIMER_MODE_ABS) == -ETIME) + __apic_timer_expired(timer); } /*