Re: [PATCH 4/8] KVM: avoid unnecessary wait for a async pf

2010-10-28 Thread Xiao Guangrong 
On 10/27/2010 06:42 PM, Gleb Natapov wrote:
 On Wed, Oct 27, 2010 at 05:04:58PM +0800, Xiao Guangrong wrote:
 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

 Correct, but it can be fixed by adding vcpu-arch.apf.halted = false; to
 kvm_arch_async_page_present(), no?
 Adding kvm_check_async_pf_completion() to arch independent kvm_vcpu_block()
 constrains how other archs may implement async pf support IMO.
  

Um, i think it's reasonable, will fix it address your comment.
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[PATCH 4/8] KVM: avoid unnecessary wait for a async pf

2010-10-27 Thread Xiao Guangrong 
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 xiaoguangr...@cn.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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Re: [PATCH 4/8] KVM: avoid unnecessary wait for a async pf

2010-10-27 Thread Gleb Natapov 
On Wed, Oct 27, 2010 at 05:04:58PM +0800, Xiao Guangrong wrote:
 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
 
Correct, but it can be fixed by adding vcpu-arch.apf.halted = false; to
kvm_arch_async_page_present(), no?
Adding kvm_check_async_pf_completion() to arch independent kvm_vcpu_block()
constrains how other archs may implement async pf support IMO.
 
 Fixed by move the check into wait context
 
 Signed-off-by: Xiao Guangrong xiaoguangr...@cn.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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