* [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq
2015-04-08 23:33 [patch -rt 0/2] use simple waitqueue for kvm vcpu waitqueue (v5) Marcelo Tosatti
@ 2015-04-08 23:33 ` Marcelo Tosatti
2015-04-08 23:33 ` [patch -rt 2/2] KVM: lapic: mark LAPIC timer handler as irqsafe Marcelo Tosatti
2015-04-09 13:18 ` [patch -rt 0/2] use simple waitqueue for kvm vcpu waitqueue (v5) Sebastian Andrzej Siewior
2 siblings, 0 replies; 4+ messages in thread
From: Marcelo Tosatti @ 2015-04-08 23:33 UTC (permalink / raw)
To: Sebastian Andrzej Siewior
Cc: Rik van Riel, Luiz Capitulino, linux-rt-users, kvm,
Marcelo Tosatti
[-- Attachment #1: kvm-use-simplewaitqueue-1 --]
[-- Type: text/plain, Size: 10348 bytes --]
The problem:
On -RT, an emulated LAPIC timer instances has the following path:
1) hard interrupt
2) ksoftirqd is scheduled
3) ksoftirqd wakes up vcpu thread
4) vcpu thread is scheduled
This extra context switch introduces unnecessary latency in the
LAPIC path for a KVM guest.
The solution:
Allow waking up vcpu thread from hardirq context,
thus avoiding the need for ksoftirqd to be scheduled.
Normal waitqueues make use of spinlocks, which on -RT
are sleepable locks. Therefore, waking up a waitqueue
waiter involves locking a sleeping lock, which
is not allowed from hard interrupt context.
cyclictest command line:
# cyclictest -m -n -q -p99 -l 1000000 -h60 -D 1m
This patch reduces the average latency in my tests from 14us to 11us.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
---
arch/arm/kvm/arm.c | 4 ++--
arch/arm/kvm/psci.c | 4 ++--
arch/powerpc/include/asm/kvm_host.h | 4 ++--
arch/powerpc/kvm/book3s_hv.c | 20 ++++++++++----------
arch/s390/include/asm/kvm_host.h | 2 +-
arch/s390/kvm/interrupt.c | 8 ++++----
arch/x86/kvm/lapic.c | 6 +++---
include/linux/kvm_host.h | 4 ++--
virt/kvm/async_pf.c | 4 ++--
virt/kvm/kvm_main.c | 16 ++++++++--------
10 files changed, 36 insertions(+), 36 deletions(-)
Index: rt-linux/arch/arm/kvm/arm.c
===================================================================
--- rt-linux.orig/arch/arm/kvm/arm.c 2015-04-08 20:20:39.962649422 -0300
+++ rt-linux/arch/arm/kvm/arm.c 2015-04-08 20:20:41.966654408 -0300
@@ -441,9 +441,9 @@
static void vcpu_pause(struct kvm_vcpu *vcpu)
{
- wait_queue_head_t *wq = kvm_arch_vcpu_wq(vcpu);
+ struct swait_head *wq = kvm_arch_vcpu_wq(vcpu);
- wait_event_interruptible(*wq, !vcpu->arch.pause);
+ swait_event_interruptible(*wq, !vcpu->arch.pause);
}
static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu)
Index: rt-linux/arch/arm/kvm/psci.c
===================================================================
--- rt-linux.orig/arch/arm/kvm/psci.c 2015-04-08 20:20:39.962649422 -0300
+++ rt-linux/arch/arm/kvm/psci.c 2015-04-08 20:20:41.966654408 -0300
@@ -66,7 +66,7 @@
{
struct kvm *kvm = source_vcpu->kvm;
struct kvm_vcpu *vcpu = NULL, *tmp;
- wait_queue_head_t *wq;
+ struct swait_head *wq;
unsigned long cpu_id;
unsigned long context_id;
unsigned long mpidr;
@@ -123,7 +123,7 @@
smp_mb(); /* Make sure the above is visible */
wq = kvm_arch_vcpu_wq(vcpu);
- wake_up_interruptible(wq);
+ swait_wake_interruptible(wq);
return PSCI_RET_SUCCESS;
}
Index: rt-linux/arch/powerpc/include/asm/kvm_host.h
===================================================================
--- rt-linux.orig/arch/powerpc/include/asm/kvm_host.h 2015-04-08 20:20:39.963649425 -0300
+++ rt-linux/arch/powerpc/include/asm/kvm_host.h 2015-04-08 20:20:41.966654408 -0300
@@ -296,7 +296,7 @@
u8 in_guest;
struct list_head runnable_threads;
spinlock_t lock;
- wait_queue_head_t wq;
+ struct swait_head wq;
u64 stolen_tb;
u64 preempt_tb;
struct kvm_vcpu *runner;
@@ -618,7 +618,7 @@
u8 prodded;
u32 last_inst;
- wait_queue_head_t *wqp;
+ struct swait_head *wqp;
struct kvmppc_vcore *vcore;
int ret;
int trap;
Index: rt-linux/arch/powerpc/kvm/book3s_hv.c
===================================================================
--- rt-linux.orig/arch/powerpc/kvm/book3s_hv.c 2015-04-08 20:20:39.964649427 -0300
+++ rt-linux/arch/powerpc/kvm/book3s_hv.c 2015-04-08 20:20:41.966654408 -0300
@@ -84,11 +84,11 @@
{
int me;
int cpu = vcpu->cpu;
- wait_queue_head_t *wqp;
+ struct swait_head *wqp;
wqp = kvm_arch_vcpu_wq(vcpu);
- if (waitqueue_active(wqp)) {
- wake_up_interruptible(wqp);
+ if (swaitqueue_active(wqp)) {
+ swait_wake_interruptible(wqp);
++vcpu->stat.halt_wakeup;
}
@@ -639,8 +639,8 @@
tvcpu->arch.prodded = 1;
smp_mb();
if (vcpu->arch.ceded) {
- if (waitqueue_active(&vcpu->wq)) {
- wake_up_interruptible(&vcpu->wq);
+ if (swaitqueue_active(&vcpu->wq)) {
+ swait_wake_interruptible(&vcpu->wq);
vcpu->stat.halt_wakeup++;
}
}
@@ -1357,7 +1357,7 @@
INIT_LIST_HEAD(&vcore->runnable_threads);
spin_lock_init(&vcore->lock);
- init_waitqueue_head(&vcore->wq);
+ init_swait_head(&vcore->wq);
vcore->preempt_tb = TB_NIL;
vcore->lpcr = kvm->arch.lpcr;
vcore->first_vcpuid = core * threads_per_subcore;
@@ -1826,13 +1826,13 @@
*/
static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
{
- DEFINE_WAIT(wait);
+ DEFINE_SWAITER(wait);
- prepare_to_wait(&vc->wq, &wait, TASK_INTERRUPTIBLE);
+ swait_prepare(&vc->wq, &wait, TASK_INTERRUPTIBLE);
vc->vcore_state = VCORE_SLEEPING;
spin_unlock(&vc->lock);
schedule();
- finish_wait(&vc->wq, &wait);
+ swait_finish(&vc->wq, &wait);
spin_lock(&vc->lock);
vc->vcore_state = VCORE_INACTIVE;
}
@@ -1873,7 +1873,7 @@
kvmppc_create_dtl_entry(vcpu, vc);
kvmppc_start_thread(vcpu);
} else if (vc->vcore_state == VCORE_SLEEPING) {
- wake_up(&vc->wq);
+ swait_wake(&vc->wq);
}
}
Index: rt-linux/arch/s390/include/asm/kvm_host.h
===================================================================
--- rt-linux.orig/arch/s390/include/asm/kvm_host.h 2015-04-08 20:20:39.964649427 -0300
+++ rt-linux/arch/s390/include/asm/kvm_host.h 2015-04-08 20:20:41.967654410 -0300
@@ -311,7 +311,7 @@
struct list_head list;
atomic_t active;
struct kvm_s390_float_interrupt *float_int;
- wait_queue_head_t *wq;
+ struct swait_head *wq;
atomic_t *cpuflags;
unsigned int action_bits;
};
Index: rt-linux/arch/s390/kvm/interrupt.c
===================================================================
--- rt-linux.orig/arch/s390/kvm/interrupt.c 2015-04-08 20:20:39.965649430 -0300
+++ rt-linux/arch/s390/kvm/interrupt.c 2015-04-08 20:20:41.967654410 -0300
@@ -619,13 +619,13 @@
void kvm_s390_vcpu_wakeup(struct kvm_vcpu *vcpu)
{
- if (waitqueue_active(&vcpu->wq)) {
+ if (swaitqueue_active(&vcpu->wq)) {
/*
* The vcpu gave up the cpu voluntarily, mark it as a good
* yield-candidate.
*/
vcpu->preempted = true;
- wake_up_interruptible(&vcpu->wq);
+ swait_wake_interruptible(&vcpu->wq);
vcpu->stat.halt_wakeup++;
}
}
@@ -736,7 +736,7 @@
spin_lock(&li->lock);
list_add(&inti->list, &li->list);
atomic_set(&li->active, 1);
- BUG_ON(waitqueue_active(li->wq));
+ BUG_ON(swaitqueue_active(li->wq));
spin_unlock(&li->lock);
return 0;
}
@@ -761,7 +761,7 @@
spin_lock(&li->lock);
list_add(&inti->list, &li->list);
atomic_set(&li->active, 1);
- BUG_ON(waitqueue_active(li->wq));
+ BUG_ON(swaitqueue_active(li->wq));
spin_unlock(&li->lock);
return 0;
}
Index: rt-linux/arch/x86/kvm/lapic.c
===================================================================
--- rt-linux.orig/arch/x86/kvm/lapic.c 2015-04-08 20:20:39.965649430 -0300
+++ rt-linux/arch/x86/kvm/lapic.c 2015-04-08 20:20:41.000000000 -0300
@@ -1539,7 +1539,7 @@
struct kvm_timer *ktimer = container_of(data, struct kvm_timer, timer);
struct kvm_lapic *apic = container_of(ktimer, struct kvm_lapic, lapic_timer);
struct kvm_vcpu *vcpu = apic->vcpu;
- wait_queue_head_t *q = &vcpu->wq;
+ struct swait_head *q = &vcpu->wq;
/*
* There is a race window between reading and incrementing, but we do
@@ -1553,8 +1553,8 @@
kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
}
- if (waitqueue_active(q))
- wake_up_interruptible(q);
+ if (swaitqueue_active(q))
+ swait_wake_interruptible(q);
if (lapic_is_periodic(apic)) {
hrtimer_add_expires_ns(&ktimer->timer, ktimer->period);
Index: rt-linux/include/linux/kvm_host.h
===================================================================
--- rt-linux.orig/include/linux/kvm_host.h 2015-04-08 20:20:39.966649432 -0300
+++ rt-linux/include/linux/kvm_host.h 2015-04-08 20:20:41.967654410 -0300
@@ -244,7 +244,7 @@
int fpu_active;
int guest_fpu_loaded, guest_xcr0_loaded;
- wait_queue_head_t wq;
+ struct swait_head wq;
struct pid *pid;
int sigset_active;
sigset_t sigset;
@@ -687,7 +687,7 @@
}
#endif
-static inline wait_queue_head_t *kvm_arch_vcpu_wq(struct kvm_vcpu *vcpu)
+static inline struct swait_head *kvm_arch_vcpu_wq(struct kvm_vcpu *vcpu)
{
#ifdef __KVM_HAVE_ARCH_WQP
return vcpu->arch.wqp;
Index: rt-linux/virt/kvm/async_pf.c
===================================================================
--- rt-linux.orig/virt/kvm/async_pf.c 2015-04-08 20:20:39.966649432 -0300
+++ rt-linux/virt/kvm/async_pf.c 2015-04-08 20:20:41.968654413 -0300
@@ -94,8 +94,8 @@
trace_kvm_async_pf_completed(addr, gva);
- if (waitqueue_active(&vcpu->wq))
- wake_up_interruptible(&vcpu->wq);
+ if (swaitqueue_active(&vcpu->wq))
+ swait_wake_interruptible(&vcpu->wq);
mmput(mm);
kvm_put_kvm(vcpu->kvm);
Index: rt-linux/virt/kvm/kvm_main.c
===================================================================
--- rt-linux.orig/virt/kvm/kvm_main.c 2015-04-08 20:20:39.966649432 -0300
+++ rt-linux/virt/kvm/kvm_main.c 2015-04-08 20:20:41.968654413 -0300
@@ -221,7 +221,7 @@
vcpu->kvm = kvm;
vcpu->vcpu_id = id;
vcpu->pid = NULL;
- init_waitqueue_head(&vcpu->wq);
+ init_swait_head(&vcpu->wq);
kvm_async_pf_vcpu_init(vcpu);
page = alloc_page(GFP_KERNEL | __GFP_ZERO);
@@ -1740,10 +1740,10 @@
*/
void kvm_vcpu_block(struct kvm_vcpu *vcpu)
{
- DEFINE_WAIT(wait);
+ DEFINE_SWAITER(wait);
for (;;) {
- prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
+ swait_prepare(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
if (kvm_arch_vcpu_runnable(vcpu)) {
kvm_make_request(KVM_REQ_UNHALT, vcpu);
@@ -1757,7 +1757,7 @@
schedule();
}
- finish_wait(&vcpu->wq, &wait);
+ swait_finish(&vcpu->wq, &wait);
}
EXPORT_SYMBOL_GPL(kvm_vcpu_block);
@@ -1769,11 +1769,11 @@
{
int me;
int cpu = vcpu->cpu;
- wait_queue_head_t *wqp;
+ struct swait_head *wqp;
wqp = kvm_arch_vcpu_wq(vcpu);
- if (waitqueue_active(wqp)) {
- wake_up_interruptible(wqp);
+ if (swaitqueue_active(wqp)) {
+ swait_wake_interruptible(wqp);
++vcpu->stat.halt_wakeup;
}
@@ -1878,7 +1878,7 @@
continue;
if (vcpu == me)
continue;
- if (waitqueue_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu))
+ if (swaitqueue_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu))
continue;
if (!kvm_vcpu_eligible_for_directed_yield(vcpu))
continue;
^ permalink raw reply [flat|nested] 4+ messages in thread* [patch -rt 2/2] KVM: lapic: mark LAPIC timer handler as irqsafe
2015-04-08 23:33 [patch -rt 0/2] use simple waitqueue for kvm vcpu waitqueue (v5) Marcelo Tosatti
2015-04-08 23:33 ` [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq Marcelo Tosatti
@ 2015-04-08 23:33 ` Marcelo Tosatti
2015-04-09 13:18 ` [patch -rt 0/2] use simple waitqueue for kvm vcpu waitqueue (v5) Sebastian Andrzej Siewior
2 siblings, 0 replies; 4+ messages in thread
From: Marcelo Tosatti @ 2015-04-08 23:33 UTC (permalink / raw)
To: Sebastian Andrzej Siewior
Cc: Rik van Riel, Luiz Capitulino, linux-rt-users, kvm,
Marcelo Tosatti
[-- Attachment #1: kvm-use-simplewaitqueue-2-lapic --]
[-- Type: text/plain, Size: 2794 bytes --]
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 <mtosatti@redhat.com>
---
arch/x86/kvm/lapic.c | 42 +++++++++++++++++++++++++++++++++++++++---
1 file changed, 39 insertions(+), 3 deletions(-)
Index: rt-linux/arch/x86/kvm/lapic.c
===================================================================
--- rt-linux.orig/arch/x86/kvm/lapic.c 2015-04-08 20:20:41.000000000 -0300
+++ rt-linux/arch/x86/kvm/lapic.c 2015-04-08 20:21:16.592739674 -0300
@@ -1034,8 +1034,38 @@
apic->divide_count);
}
+
+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);
@@ -1065,9 +1095,11 @@
}
}
- 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 ", "
@@ -1097,8 +1129,10 @@
ns = (tscdeadline - guest_tsc) * 1000000ULL;
do_div(ns, this_tsc_khz);
}
- hrtimer_start(&apic->lapic_timer.timer,
+ ret = hrtimer_start(&apic->lapic_timer.timer,
ktime_add_ns(now, ns), HRTIMER_MODE_ABS);
+ if (ret == -ETIME)
+ apic_timer_expired(&apic->lapic_timer.timer);
local_irq_restore(flags);
}
@@ -1587,6 +1621,7 @@
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
@@ -1707,7 +1742,8 @@
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);
}
/*
^ permalink raw reply [flat|nested] 4+ messages in thread