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authorDavidlohr Bueso <dave@stgolabs.net>2020-04-23 22:48:37 -0700
committerPaolo Bonzini <pbonzini@redhat.com>2020-05-13 12:14:56 -0400
commitda4ad88cab5867ee240dfd0585e9d115a8cc47db (patch)
treeb145ec0dedb065d2633ba62466cc5c7232a894af
parent191a43be61d6791fd4a9098a35c1a09e73f55228 (diff)
downloadlinux-da4ad88cab5867ee240dfd0585e9d115a8cc47db.tar.bz2
kvm: Replace vcpu->swait with rcuwait
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 modifying the queue. This also applies to per-vcore wait for powerpc kvm-hv. The x86 tscdeadline_latency test mentioned in 8577370fb0cb ("KVM: Use simple waitqueue for vcpu->wq") shows that, on avg, latency is reduced by around 15-20% with this change. Cc: Paul Mackerras <paulus@ozlabs.org> Cc: kvmarm@lists.cs.columbia.edu Cc: linux-mips@vger.kernel.org Reviewed-by: Marc Zyngier <maz@kernel.org> Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Message-Id: <20200424054837.5138-6-dave@stgolabs.net> [Avoid extra logic changes. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r--arch/mips/kvm/mips.c6
-rw-r--r--arch/powerpc/include/asm/kvm_book3s.h2
-rw-r--r--arch/powerpc/include/asm/kvm_host.h2
-rw-r--r--arch/powerpc/kvm/book3s_hv.c23
-rw-r--r--arch/powerpc/kvm/powerpc.c2
-rw-r--r--arch/x86/kvm/lapic.c2
-rw-r--r--include/linux/kvm_host.h10
-rw-r--r--virt/kvm/arm/arch_timer.c3
-rw-r--r--virt/kvm/arm/arm.c9
-rw-r--r--virt/kvm/async_pf.c3
-rw-r--r--virt/kvm/kvm_main.c19
11 files changed, 38 insertions, 43 deletions
diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index 9f50ceef9978..9787cdec33e6 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -283,8 +283,7 @@ static enum hrtimer_restart kvm_mips_comparecount_wakeup(struct hrtimer *timer)
kvm_mips_callbacks->queue_timer_int(vcpu);
vcpu->arch.wait = 0;
- if (swq_has_sleeper(&vcpu->wq))
- swake_up_one(&vcpu->wq);
+ rcuwait_wake_up(&vcpu->wait);
return kvm_mips_count_timeout(vcpu);
}
@@ -511,8 +510,7 @@ int kvm_vcpu_ioctl_interrupt(struct kvm_vcpu *vcpu,
dvcpu->arch.wait = 0;
- if (swq_has_sleeper(&dvcpu->wq))
- swake_up_one(&dvcpu->wq);
+ rcuwait_wake_up(&dvcpu->wait);
return 0;
}
diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h
index 506e4df2d730..6e5d85ba588d 100644
--- a/arch/powerpc/include/asm/kvm_book3s.h
+++ b/arch/powerpc/include/asm/kvm_book3s.h
@@ -78,7 +78,7 @@ struct kvmppc_vcore {
struct kvm_vcpu *runnable_threads[MAX_SMT_THREADS];
struct list_head preempt_list;
spinlock_t lock;
- struct swait_queue_head wq;
+ struct rcuwait wait;
spinlock_t stoltb_lock; /* protects stolen_tb and preempt_tb */
u64 stolen_tb;
u64 preempt_tb;
diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 1dc63101ffe1..337047ba4a56 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -751,7 +751,7 @@ 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 93493f0cbfe8..7f59c47a5b9d 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -230,13 +230,11 @@ 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 *waitp;
- wqp = kvm_arch_vcpu_wq(vcpu);
- if (swq_has_sleeper(wqp)) {
- swake_up_one(wqp);
+ waitp = kvm_arch_vcpu_get_wait(vcpu);
+ if (rcuwait_wake_up(waitp))
++vcpu->stat.halt_wakeup;
- }
cpu = READ_ONCE(vcpu->arch.thread_cpu);
if (cpu >= 0 && kvmppc_ipi_thread(cpu))
@@ -2125,7 +2123,7 @@ static struct kvmppc_vcore *kvmppc_vcore_create(struct kvm *kvm, int id)
spin_lock_init(&vcore->lock);
spin_lock_init(&vcore->stoltb_lock);
- init_swait_queue_head(&vcore->wq);
+ rcuwait_init(&vcore->wait);
vcore->preempt_tb = TB_NIL;
vcore->lpcr = kvm->arch.lpcr;
vcore->first_vcpuid = id;
@@ -3784,7 +3782,6 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
ktime_t cur, start_poll, start_wait;
int do_sleep = 1;
u64 block_ns;
- DECLARE_SWAITQUEUE(wait);
/* Poll for pending exceptions and ceded state */
cur = start_poll = ktime_get();
@@ -3812,10 +3809,10 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
}
}
- prepare_to_swait_exclusive(&vc->wq, &wait, TASK_INTERRUPTIBLE);
-
+ prepare_to_rcuwait(&vc->wait);
+ set_current_state(TASK_INTERRUPTIBLE);
if (kvmppc_vcore_check_block(vc)) {
- finish_swait(&vc->wq, &wait);
+ finish_rcuwait(&vc->wait);
do_sleep = 0;
/* If we polled, count this as a successful poll */
if (vc->halt_poll_ns)
@@ -3829,7 +3826,7 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
trace_kvmppc_vcore_blocked(vc, 0);
spin_unlock(&vc->lock);
schedule();
- finish_swait(&vc->wq, &wait);
+ finish_rcuwait(&vc->wait);
spin_lock(&vc->lock);
vc->vcore_state = VCORE_INACTIVE;
trace_kvmppc_vcore_blocked(vc, 1);
@@ -3940,7 +3937,7 @@ static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
kvmppc_start_thread(vcpu, vc);
trace_kvm_guest_enter(vcpu);
} else if (vc->vcore_state == VCORE_SLEEPING) {
- swake_up_one(&vc->wq);
+ rcuwait_wake_up(&vc->wait);
}
}
@@ -4279,7 +4276,7 @@ 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/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 052614e9d468..27ccff612903 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -752,7 +752,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
if (err)
goto out_vcpu_uninit;
- vcpu->arch.wqp = &vcpu->wq;
+ vcpu->arch.waitp = &vcpu->wait;
kvmppc_create_vcpu_debugfs(vcpu, vcpu->vcpu_id);
return 0;
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 38f7dc9c16ee..42cd2e3ec6fd 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1861,7 +1861,7 @@ 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(rcuwait_active(&vcpu->wait));
cancel_hv_timer(apic);
apic_timer_expired(apic);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index abfa71cb5d2d..161684696610 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;
@@ -960,12 +960,12 @@ 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.waitp;
#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 93bd59b46848..d5024416e722 100644
--- a/virt/kvm/arm/arch_timer.c
+++ b/virt/kvm/arm/arch_timer.c
@@ -571,6 +571,7 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu)
{
struct arch_timer_cpu *timer = vcpu_timer(vcpu);
struct timer_map map;
+ struct rcuwait *wait = kvm_arch_vcpu_get_wait(vcpu);
if (unlikely(!timer->enabled))
return;
@@ -593,7 +594,7 @@ 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 (rcuwait_active(wait))
kvm_timer_blocking(vcpu);
/*
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index f5390ac2165b..d5db0d6141ff 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 7525f3838160..e12317f32c5e 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -349,7 +349,7 @@ 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;
@@ -2678,7 +2678,6 @@ out:
void kvm_vcpu_block(struct kvm_vcpu *vcpu)
{
ktime_t start, cur;
- DECLARE_SWAITQUEUE(wait);
bool waited = false;
u64 block_ns;
@@ -2704,8 +2703,9 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
} while (single_task_running() && ktime_before(cur, stop));
}
+ prepare_to_rcuwait(&vcpu->wait);
for (;;) {
- prepare_to_swait_exclusive(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
+ set_current_state(TASK_INTERRUPTIBLE);
if (kvm_vcpu_check_block(vcpu) < 0)
break;
@@ -2713,8 +2713,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
waited = true;
schedule();
}
-
- finish_swait(&vcpu->wq, &wait);
+ finish_rcuwait(&vcpu->wait);
cur = ktime_get();
out:
kvm_arch_vcpu_unblocking(vcpu);
@@ -2746,11 +2745,10 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_block);
bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu)
{
- struct swait_queue_head *wqp;
+ struct rcuwait *waitp;
- wqp = kvm_arch_vcpu_wq(vcpu);
- if (swq_has_sleeper(wqp)) {
- swake_up_one(wqp);
+ waitp = kvm_arch_vcpu_get_wait(vcpu);
+ if (rcuwait_wake_up(waitp)) {
WRITE_ONCE(vcpu->ready, true);
++vcpu->stat.halt_wakeup;
return true;
@@ -2892,7 +2890,8 @@ 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 (rcuwait_active(&vcpu->wait) &&
+ !vcpu_dy_runnable(vcpu))
continue;
if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode &&
!kvm_arch_vcpu_in_kernel(vcpu))