linux-kernel - [PATCH 4/8] KVM: avoid unnecessary wait for a async pf

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Date:	Wed, 27 Oct 2010 17:04:58 +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 4/8] KVM: avoid unnecessary wait for a async pf

In current code, it checks async pf completion out of the wait context,
like this:

if (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
		    !vcpu->arch.apf.halted)
			r = vcpu_enter_guest(vcpu);
		else {
			......
			kvm_vcpu_block(vcpu)
			 ^- waiting until 'async_pf.done' is not empty
}
	
kvm_check_async_pf_completion(vcpu)
 ^- delete list from async_pf.done

So, if we check aysnc pf completion first, it can be blocked at
kvm_vcpu_block

Fixed by move the check into wait context

Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
---
 arch/x86/kvm/x86.c       |    3 ---
 include/linux/kvm_host.h |    1 -
 virt/kvm/async_pf.c      |    6 ++++--
 virt/kvm/async_pf.h      |    6 ++++++
 virt/kvm/kvm_main.c      |    3 ++-
 5 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 16f42ff..0b2c420 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5321,8 +5321,6 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 			vcpu->run->exit_reason = KVM_EXIT_INTR;
 			++vcpu->stat.request_irq_exits;
 		}
-		
-		kvm_check_async_pf_completion(vcpu);
 
 		if (signal_pending(current)) {
 			r = -EINTR;
@@ -6108,7 +6106,6 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
 {
 	return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
 		!vcpu->arch.apf.halted)
-		|| !list_empty_careful(&vcpu->async_pf.done)
 		|| vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED
 		|| vcpu->arch.nmi_pending ||
 		(kvm_arch_interrupt_allowed(vcpu) &&
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index ee4314e..0c1b7c5 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -90,7 +90,6 @@ struct kvm_async_pf {
 };
 
 void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu);
-void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu);
 int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn,
 		       struct kvm_arch_async_pf *arch);
 int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 60df9e0..e213ca4 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -120,13 +120,13 @@ void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu)
 	vcpu->async_pf.queued = 0;
 }
 
-void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
+bool kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
 {
 	struct kvm_async_pf *work;
 
 	if (list_empty_careful(&vcpu->async_pf.done) ||
 	    !kvm_arch_can_inject_async_page_present(vcpu))
-		return;
+		return false;
 
 	spin_lock(&vcpu->async_pf.lock);
 	work = list_first_entry(&vcpu->async_pf.done, typeof(*work), link);
@@ -142,6 +142,8 @@ void kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
 	if (work->page)
 		put_page(work->page);
 	kmem_cache_free(async_pf_cache, work);
+
+	return true;
 }
 
 int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn,
diff --git a/virt/kvm/async_pf.h b/virt/kvm/async_pf.h
index e7ef644..e21533c 100644
--- a/virt/kvm/async_pf.h
+++ b/virt/kvm/async_pf.h
@@ -27,10 +27,16 @@
 int kvm_async_pf_init(void);
 void kvm_async_pf_deinit(void);
 void kvm_async_pf_vcpu_init(struct kvm_vcpu *vcpu);
+bool kvm_check_async_pf_completion(struct kvm_vcpu *vcpu);
+
 #else
 #define kvm_async_pf_init() (0)
 #define kvm_async_pf_deinit() do{}while(0)
 #define kvm_async_pf_vcpu_init(C) do{}while(0)
+static inline bool kvm_check_async_pf_completion(struct kvm_vcpu *vcpu)
+{
+	return false;
+}
 #endif
 
 #endif
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 88d869e..d9aed28 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1347,7 +1347,8 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
 	for (;;) {
 		prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
 
-		if (kvm_arch_vcpu_runnable(vcpu)) {
+		if (kvm_arch_vcpu_runnable(vcpu) ||
+		     kvm_check_async_pf_completion(vcpu)) {
 			kvm_make_request(KVM_REQ_UNHALT, vcpu);
 			break;
 		}
-- 
1.7.0.4

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