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Subject[PATCH v2 1/3] KVM: LAPIC: Make lapic timer unpinned when timer is injected by posted-interrupt
Date
From: Wanpeng Li <wanpengli@tencent.com>

Make lapic timer unpinned when timer is injected by posted-interrupt,
the emulated timer can be offload to the housekeeping cpus.

The host admin should fine tuned, e.g. dedicated instances scenario
w/ nohz_full cover the pCPUs which vCPUs resident, several pCPUs
surplus for housekeeping, disable mwait/hlt/pause vmexits to occupy
the pCPUs, fortunately preemption timer is disabled after mwait is
exposed to guest which makes emulated timer offload can be possible.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
arch/x86/kvm/lapic.c | 20 ++++++++++++++++----
arch/x86/kvm/x86.c | 5 +++++
arch/x86/kvm/x86.h | 2 ++
include/linux/sched/isolation.h | 2 ++
kernel/sched/isolation.c | 6 ++++++
5 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index fcf42a3..09b7387 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -127,6 +127,12 @@ static inline u32 kvm_x2apic_id(struct kvm_lapic *apic)
return apic->vcpu->vcpu_id;
}

+static inline bool posted_interrupt_inject_timer_enabled(struct kvm_vcpu *vcpu)
+{
+ return pi_inject_timer && kvm_vcpu_apicv_active(vcpu) &&
+ kvm_mwait_in_guest(vcpu->kvm);
+}
+
static inline bool kvm_apic_map_get_logical_dest(struct kvm_apic_map *map,
u32 dest_id, struct kvm_lapic ***cluster, u16 *mask) {
switch (map->mode) {
@@ -1581,7 +1587,9 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic)
likely(ns > apic->lapic_timer.timer_advance_ns)) {
expire = ktime_add_ns(now, ns);
expire = ktime_sub_ns(expire, ktimer->timer_advance_ns);
- hrtimer_start(&ktimer->timer, expire, HRTIMER_MODE_ABS_PINNED);
+ hrtimer_start(&ktimer->timer, expire,
+ posted_interrupt_inject_timer_enabled(vcpu) ?
+ HRTIMER_MODE_ABS : HRTIMER_MODE_ABS_PINNED);
} else
apic_timer_expired(apic);

@@ -1683,7 +1691,8 @@ static void start_sw_period(struct kvm_lapic *apic)

hrtimer_start(&apic->lapic_timer.timer,
apic->lapic_timer.target_expiration,
- HRTIMER_MODE_ABS_PINNED);
+ posted_interrupt_inject_timer_enabled(apic->vcpu) ?
+ HRTIMER_MODE_ABS : HRTIMER_MODE_ABS_PINNED);
}

bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu)
@@ -2320,7 +2329,8 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, int timer_advance_ns)
apic->vcpu = vcpu;

hrtimer_init(&apic->lapic_timer.timer, CLOCK_MONOTONIC,
- HRTIMER_MODE_ABS_PINNED);
+ posted_interrupt_inject_timer_enabled(vcpu) ?
+ HRTIMER_MODE_ABS : HRTIMER_MODE_ABS_PINNED);
apic->lapic_timer.timer.function = apic_timer_fn;
if (timer_advance_ns == -1) {
apic->lapic_timer.timer_advance_ns = 1000;
@@ -2509,7 +2519,9 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)

timer = &vcpu->arch.apic->lapic_timer.timer;
if (hrtimer_cancel(timer))
- hrtimer_start_expires(timer, HRTIMER_MODE_ABS_PINNED);
+ hrtimer_start_expires(timer,
+ posted_interrupt_inject_timer_enabled(vcpu) ?
+ HRTIMER_MODE_ABS : HRTIMER_MODE_ABS_PINNED);
}

/*
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6200d5a..2ef2394 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -54,6 +54,7 @@
#include <linux/kvm_irqfd.h>
#include <linux/irqbypass.h>
#include <linux/sched/stat.h>
+#include <linux/sched/isolation.h>
#include <linux/mem_encrypt.h>

#include <trace/events/kvm.h>
@@ -155,6 +156,9 @@ EXPORT_SYMBOL_GPL(enable_vmware_backdoor);
static bool __read_mostly force_emulation_prefix = false;
module_param(force_emulation_prefix, bool, S_IRUGO);

+bool __read_mostly pi_inject_timer = 0;
+module_param(pi_inject_timer, bool, S_IRUGO | S_IWUSR);
+
#define KVM_NR_SHARED_MSRS 16

struct kvm_shared_msrs_global {
@@ -7030,6 +7034,7 @@ int kvm_arch_init(void *opaque)
host_xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);

kvm_lapic_init();
+ pi_inject_timer = housekeeping_enabled(HK_FLAG_TIMER);
#ifdef CONFIG_X86_64
pvclock_gtod_register_notifier(&pvclock_gtod_notifier);

diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 275b3b6..aa539d6 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -296,6 +296,8 @@ extern unsigned int min_timer_period_us;

extern bool enable_vmware_backdoor;

+extern bool pi_inject_timer;
+
extern struct static_key kvm_no_apic_vcpu;

static inline u64 nsec_to_cycles(struct kvm_vcpu *vcpu, u64 nsec)
diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index b0fb144..6fc5407 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -19,6 +19,7 @@ enum hk_flags {
DECLARE_STATIC_KEY_FALSE(housekeeping_overridden);
extern int housekeeping_any_cpu(enum hk_flags flags);
extern const struct cpumask *housekeeping_cpumask(enum hk_flags flags);
+extern bool housekeeping_enabled(enum hk_flags flags);
extern void housekeeping_affine(struct task_struct *t, enum hk_flags flags);
extern bool housekeeping_test_cpu(int cpu, enum hk_flags flags);
extern void __init housekeeping_init(void);
@@ -38,6 +39,7 @@ static inline const struct cpumask *housekeeping_cpumask(enum hk_flags flags)
static inline void housekeeping_affine(struct task_struct *t,
enum hk_flags flags) { }
static inline void housekeeping_init(void) { }
+static inline bool housekeeping_enabled(enum hk_flags flags) { }
#endif /* CONFIG_CPU_ISOLATION */

static inline bool housekeeping_cpu(int cpu, enum hk_flags flags)
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 123ea07..ccb2808 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -14,6 +14,12 @@ EXPORT_SYMBOL_GPL(housekeeping_overridden);
static cpumask_var_t housekeeping_mask;
static unsigned int housekeeping_flags;

+bool housekeeping_enabled(enum hk_flags flags)
+{
+ return !!(housekeeping_flags & flags);
+}
+EXPORT_SYMBOL_GPL(housekeeping_enabled);
+
int housekeeping_any_cpu(enum hk_flags flags)
{
if (static_branch_unlikely(&housekeeping_overridden))
--
2.7.4
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