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Date: Wed, 12 Jan 2011 15:40:31 +0800
From: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To: Avi Kivity <avi@...hat.com>
CC: Marcelo Tosatti <mtosatti@...hat.com>,
LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: [PATCH v3 2/3] KVM: send IPI to vcpu only when it's in guest mode
We can interrupt the vcpu only when it's running in guest mode
to reduce IPI
Also
1: No need atomically to read/write ->mode in vcpu's thread
2: reorganize struct kvm_vcpu to make ->mode and ->requests
in the same cache line explicitly
Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
---
arch/ia64/kvm/kvm-ia64.c | 2 ++
arch/x86/kvm/x86.c | 16 ++++++++++------
include/linux/kvm_host.h | 22 +++++++++++++++++-----
virt/kvm/kvm_main.c | 7 ++++++-
4 files changed, 35 insertions(+), 12 deletions(-)
diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index 70d224d..8213efe 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -662,6 +662,7 @@ again:
goto vcpu_run_fail;
srcu_read_unlock(&vcpu->kvm->srcu, idx);
+ vcpu->mode = IN_GUEST_MODE;
kvm_guest_enter();
/*
@@ -683,6 +684,7 @@ again:
*/
barrier();
kvm_guest_exit();
+ vcpu->mode = OUTSIDE_GUEST_MODE;
preempt_enable();
idx = srcu_read_lock(&vcpu->kvm->srcu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0b77e9c..434363e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5213,14 +5213,18 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
kvm_load_guest_fpu(vcpu);
kvm_load_guest_xcr0(vcpu);
- atomic_set(&vcpu->guest_mode, 1);
- smp_wmb();
+ vcpu->mode = IN_GUEST_MODE;
+
+ /* We should set ->mode before check ->requests,
+ * see the comment in make_all_cpus_request.
+ */
+ smp_mb();
local_irq_disable();
- if (!atomic_read(&vcpu->guest_mode) || vcpu->requests
+ if (vcpu->mode == EXITING_GUEST_MODE || vcpu->requests
|| need_resched() || signal_pending(current)) {
- atomic_set(&vcpu->guest_mode, 0);
+ vcpu->mode = OUTSIDE_GUEST_MODE;
smp_wmb();
local_irq_enable();
preempt_enable();
@@ -5256,7 +5260,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
kvm_get_msr(vcpu, MSR_IA32_TSC, &vcpu->arch.last_guest_tsc);
- atomic_set(&vcpu->guest_mode, 0);
+ vcpu->mode = OUTSIDE_GUEST_MODE;
smp_wmb();
local_irq_enable();
@@ -6157,7 +6161,7 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
me = get_cpu();
if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu))
- if (atomic_xchg(&vcpu->guest_mode, 0))
+ if (kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE)
smp_send_reschedule(cpu);
put_cpu();
}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b5021db..b99eacd 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -98,19 +98,26 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn,
int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
#endif
+enum {
+ OUTSIDE_GUEST_MODE,
+ IN_GUEST_MODE,
+ EXITING_GUEST_MODE
+};
+
struct kvm_vcpu {
struct kvm *kvm;
#ifdef CONFIG_PREEMPT_NOTIFIERS
struct preempt_notifier preempt_notifier;
#endif
+ int cpu;
int vcpu_id;
- struct mutex mutex;
- int cpu;
- atomic_t guest_mode;
- struct kvm_run *run;
+ int srcu_idx;
+ int mode;
unsigned long requests;
unsigned long guest_debug;
- int srcu_idx;
+
+ struct mutex mutex;
+ struct kvm_run *run;
int fpu_active;
int guest_fpu_loaded, guest_xcr0_loaded;
@@ -140,6 +147,11 @@ struct kvm_vcpu {
struct kvm_vcpu_arch arch;
};
+static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
+{
+ return cmpxchg(&vcpu->mode, IN_GUEST_MODE, EXITING_GUEST_MODE);
+}
+
/*
* Some of the bitops functions do not support too long bitmaps.
* This number must be determined not to exceed such limits.
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b1b6cbb..71a4eaf 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -153,7 +153,12 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
if (kvm_make_check_request(req, vcpu))
continue;
cpu = vcpu->cpu;
- if (cpus != NULL && cpu != -1 && cpu != me)
+
+ /* Set ->requests bit before we read ->mode */
+ smp_mb();
+
+ if (cpus != NULL && cpu != -1 && cpu != me &&
+ kvm_vcpu_exiting_guest_mode(vcpu) != OUTSIDE_GUEST_MODE)
cpumask_set_cpu(cpu, cpus);
}
if (unlikely(cpus == NULL))
--
1.7.3.4
--
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