The use of any sort of waitqueue (simple or regular) for
wait/waking vcpus has always been an overkill and semantically
wrong. Because this is per-vcpu (which is blocked) there is
only ever a single waiting vcpu, thus no need for any sort of
queue.
As such, make use of the rcuwait primitive, with the following
considerations:
- rcuwait already provides the proper barriers that serialize
concurrent waiter and waker.
- Task wakeup is done in rcu read critical region, with a
stable task pointer.
- Because there is no concurrency among waiters, we need
not worry about rcuwait_wait_event() calls corrupting
the wait->task. As a consequence, this saves the locking
done in swait when adding to the queue.
The x86-tscdeadline_latency test mentioned in 8577370fb0cb
("KVM: Use simple waitqueue for vcpu->wq") shows that, on avg,
latency is reduced by around 15% with this change.
Cc: Paolo Bonzini <pbonz...@redhat.com>
Signed-off-by: Davidlohr Bueso <dbu...@suse.de>
---
Only compiled and tested on x86.
arch/powerpc/include/asm/kvm_host.h | 2 +-
arch/powerpc/kvm/book3s_hv.c | 10 ++++------
arch/x86/kvm/lapic.c | 2 +-
include/linux/kvm_host.h | 10 +++++-----
virt/kvm/arm/arch_timer.c | 2 +-
virt/kvm/arm/arm.c | 9 +++++----
virt/kvm/async_pf.c | 3 +--
virt/kvm/kvm_main.c | 33 +++++++++++++--------------------
8 files changed, 31 insertions(+), 40 deletions(-)
diff --git a/arch/powerpc/include/asm/kvm_host.h
b/arch/powerpc/include/asm/kvm_host.h
index 6e8b8ffd06ad..e2b4a1e3fb7d 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -752,7 +752,7 @@ struct kvm_vcpu_arch {
u8 irq_pending; /* Used by XIVE to signal pending guest irqs */
u32 last_inst;
- struct swait_queue_head *wqp;
+ struct rcuwait *waitp;
struct kvmppc_vcore *vcore;
int ret;
int trap;
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 2cefd071b848..c7cbc4bd06e9 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -231,13 +231,11 @@ static bool kvmppc_ipi_thread(int cpu)
static void kvmppc_fast_vcpu_kick_hv(struct kvm_vcpu *vcpu)
{
int cpu;
- struct swait_queue_head *wqp;
+ struct rcuwait *wait;
- wqp = kvm_arch_vcpu_wq(vcpu);
- if (swq_has_sleeper(wqp)) {
- swake_up_one(wqp);
+ wait = kvm_arch_vcpu_get_wait(vcpu);
+ if (rcuwait_wake_up(wait))
++vcpu->stat.halt_wakeup;
- }
cpu = READ_ONCE(vcpu->arch.thread_cpu);
if (cpu >= 0 && kvmppc_ipi_thread(cpu))
@@ -4274,7 +4272,7 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct
kvm_vcpu *vcpu)
}
user_vrsave = mfspr(SPRN_VRSAVE);
- vcpu->arch.wqp = &vcpu->arch.vcore->wq;
+ vcpu->arch.waitp = &vcpu->arch.vcore->wait;
vcpu->arch.pgdir = kvm->mm->pgd;
vcpu->arch.state = KVMPPC_VCPU_BUSY_IN_HOST;
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index e3099c642fec..a4420c26dfbc 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1815,7 +1815,7 @@ void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
/* If the preempt notifier has already run, it also called
apic_timer_expired */
if (!apic->lapic_timer.hv_timer_in_use)
goto out;
- WARN_ON(swait_active(&vcpu->wq));
+ WARN_ON(rcu_dereference(vcpu->wait.task));
cancel_hv_timer(apic);
apic_timer_expired(apic);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index bcb9b2ac0791..b5694429aede 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -23,7 +23,7 @@
#include <linux/irqflags.h>
#include <linux/context_tracking.h>
#include <linux/irqbypass.h>
-#include <linux/swait.h>
+#include <linux/rcuwait.h>
#include <linux/refcount.h>
#include <linux/nospec.h>
#include <asm/signal.h>
@@ -277,7 +277,7 @@ struct kvm_vcpu {
struct mutex mutex;
struct kvm_run *run;
- struct swait_queue_head wq;
+ struct rcuwait wait;
struct pid __rcu *pid;
int sigset_active;
sigset_t sigset;
@@ -952,12 +952,12 @@ static inline bool kvm_arch_has_assigned_device(struct
kvm *kvm)
}
#endif
-static inline struct swait_queue_head *kvm_arch_vcpu_wq(struct kvm_vcpu *vcpu)
+static inline struct rcuwait *kvm_arch_vcpu_get_wait(struct kvm_vcpu *vcpu)
{
#ifdef __KVM_HAVE_ARCH_WQP
- return vcpu->arch.wqp;
+ return vcpu->arch.wait;
#else
- return &vcpu->wq;
+ return &vcpu->wait;
#endif
}
diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
index 0d9438e9de2a..4be71cb58691 100644
--- a/virt/kvm/arm/arch_timer.c
+++ b/virt/kvm/arm/arch_timer.c
@@ -593,7 +593,7 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu)
if (map.emul_ptimer)
soft_timer_cancel(&map.emul_ptimer->hrtimer);
- if (swait_active(kvm_arch_vcpu_wq(vcpu)))
+ if (rcu_dereference(kvm_arch_vpu_get_wait(vcpu)) != NULL)
kvm_timer_blocking(vcpu);
/*
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index eda7b624eab8..4a704866e9b6 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -579,16 +579,17 @@ void kvm_arm_resume_guest(struct kvm *kvm)
kvm_for_each_vcpu(i, vcpu, kvm) {
vcpu->arch.pause = false;
- swake_up_one(kvm_arch_vcpu_wq(vcpu));
+ rcuwait_wake_up(kvm_arch_vcpu_get_wait(vcpu));
}
}
static void vcpu_req_sleep(struct kvm_vcpu *vcpu)
{
- struct swait_queue_head *wq = kvm_arch_vcpu_wq(vcpu);
+ struct rcuwait *wait = kvm_arch_vcpu_get_wait(vcpu);
- swait_event_interruptible_exclusive(*wq, ((!vcpu->arch.power_off) &&
- (!vcpu->arch.pause)));
+ rcuwait_wait_event(*wait,
+ (!vcpu->arch.power_off) && (!vcpu->arch.pause),
+ TASK_INTERRUPTIBLE);
if (vcpu->arch.power_off || vcpu->arch.pause) {
/* Awaken to handle a signal, request we sleep again later. */
diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 15e5b037f92d..10b533f641a6 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -80,8 +80,7 @@ static void async_pf_execute(struct work_struct *work)
trace_kvm_async_pf_completed(addr, cr2_or_gpa);
- if (swq_has_sleeper(&vcpu->wq))
- swake_up_one(&vcpu->wq);
+ rcuwait_wake_up(&vcpu->wait);
mmput(mm);
kvm_put_kvm(vcpu->kvm);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 70f03ce0e5c1..6b49dcb321e2 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -343,7 +343,7 @@ static void kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm
*kvm, unsigned id)
vcpu->kvm = kvm;
vcpu->vcpu_id = id;
vcpu->pid = NULL;
- init_swait_queue_head(&vcpu->wq);
+ rcuwait_init(&vcpu->wait);
kvm_async_pf_vcpu_init(vcpu);
vcpu->pre_pcpu = -1;
@@ -2465,9 +2465,8 @@ static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
void kvm_vcpu_block(struct kvm_vcpu *vcpu)
{
ktime_t start, cur;
- DECLARE_SWAITQUEUE(wait);
- bool waited = false;
u64 block_ns;
+ int block_check = -EINTR;
kvm_arch_vcpu_blocking(vcpu);
@@ -2487,21 +2486,14 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
++vcpu->stat.halt_poll_invalid;
goto out;
}
+
cur = ktime_get();
} while (single_task_running() && ktime_before(cur, stop));
}
- for (;;) {
- prepare_to_swait_exclusive(&vcpu->wq, &wait,
TASK_INTERRUPTIBLE);
-
- if (kvm_vcpu_check_block(vcpu) < 0)
- break;
-
- waited = true;
- schedule();
- }
-
- finish_swait(&vcpu->wq, &wait);
+ rcuwait_wait_event(&vcpu->wait,
+ (block_check = kvm_vcpu_check_block(vcpu)) < 0,
+ TASK_INTERRUPTIBLE);
cur = ktime_get();
out:
kvm_arch_vcpu_unblocking(vcpu);
@@ -2525,18 +2517,18 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
}
}
- trace_kvm_vcpu_wakeup(block_ns, waited, vcpu_valid_wakeup(vcpu));
+ trace_kvm_vcpu_wakeup(block_ns, block_check < 0 ? false : true,
+ vcpu_valid_wakeup(vcpu));
kvm_arch_vcpu_block_finish(vcpu);
}
EXPORT_SYMBOL_GPL(kvm_vcpu_block);
bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu)
{
- struct swait_queue_head *wqp;
+ struct rcuwait *wait;
- wqp = kvm_arch_vcpu_wq(vcpu);
- if (swq_has_sleeper(wqp)) {
- swake_up_one(wqp);
+ wait = kvm_arch_vcpu_get_wait(vcpu);
+ if (rcuwait_wake_up(wait)) {
WRITE_ONCE(vcpu->ready, true);
++vcpu->stat.halt_wakeup;
return true;
@@ -2678,7 +2670,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool
yield_to_kernel_mode)
continue;
if (vcpu == me)
continue;
- if (swait_active(&vcpu->wq) && !vcpu_dy_runnable(vcpu))
+ if (rcu_dereference(vcpu->wait.task) &&
+ !vcpu_dy_runnable(vcpu))
continue;
if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode
&&
!kvm_arch_vcpu_in_kernel(vcpu))
--
2.16.4
