[Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-05 Thread Juergen Gross 
There are cases where a guest tries to switch spinlocks to bare metal
behavior (e.g. by setting "xen_nopvspin" boot parameter). Today this
has the downside of falling back to unfair test and set scheme for
qspinlocks due to virt_spin_lock() detecting the virtualized
environment.

Make virt_spin_lock() a paravirt operation in order to enable users
to select an explicit behavior like bare metal.

Signed-off-by: Juergen Gross 
---
 arch/x86/include/asm/paravirt.h   |  5 
 arch/x86/include/asm/paravirt_types.h |  1 +
 arch/x86/include/asm/qspinlock.h  | 48 ---
 arch/x86/kernel/paravirt-spinlocks.c  | 14 ++
 arch/x86/kernel/smpboot.c |  2 ++
 5 files changed, 55 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index c25dd22f7c70..d9e954fb37df 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -725,6 +725,11 @@ static __always_inline bool pv_vcpu_is_preempted(long cpu)
return PVOP_CALLEE1(bool, pv_lock_ops.vcpu_is_preempted, cpu);
 }
 
+static __always_inline bool pv_virt_spin_lock(struct qspinlock *lock)
+{
+   return PVOP_CALLEE1(bool, pv_lock_ops.virt_spin_lock, lock);
+}
+
 #endif /* SMP && PARAVIRT_SPINLOCKS */
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/include/asm/paravirt_types.h 
b/arch/x86/include/asm/paravirt_types.h
index 19efefc0e27e..928f5e7953a7 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -319,6 +319,7 @@ struct pv_lock_ops {
void (*kick)(int cpu);
 
struct paravirt_callee_save vcpu_is_preempted;
+   struct paravirt_callee_save virt_spin_lock;
 } __no_randomize_layout;
 
 /* This contains all the paravirt structures: we get a convenient
diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
index 48a706f641f2..fbd98896385c 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -17,6 +17,25 @@ static inline void native_queued_spin_unlock(struct 
qspinlock *lock)
smp_store_release((u8 *)lock, 0);
 }
 
+static inline bool native_virt_spin_lock(struct qspinlock *lock)
+{
+   if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
+   return false;
+
+   /*
+* On hypervisors without PARAVIRT_SPINLOCKS support we fall
+* back to a Test-and-Set spinlock, because fair locks have
+* horrible lock 'holder' preemption issues.
+*/
+
+   do {
+   while (atomic_read(&lock->val) != 0)
+   cpu_relax();
+   } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
+
+   return true;
+}
+
 #ifdef CONFIG_PARAVIRT_SPINLOCKS
 extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
 extern void __pv_init_lock_hash(void);
@@ -38,33 +57,32 @@ static inline bool vcpu_is_preempted(long cpu)
 {
return pv_vcpu_is_preempted(cpu);
 }
+
+void native_pv_lock_init(void) __init;
 #else
 static inline void queued_spin_unlock(struct qspinlock *lock)
 {
native_queued_spin_unlock(lock);
 }
+
+static inline void native_pv_lock_init(void)
+{
+}
 #endif
 
 #ifdef CONFIG_PARAVIRT
 #define virt_spin_lock virt_spin_lock
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
 static inline bool virt_spin_lock(struct qspinlock *lock)
 {
-   if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
-   return false;
-
-   /*
-* On hypervisors without PARAVIRT_SPINLOCKS support we fall
-* back to a Test-and-Set spinlock, because fair locks have
-* horrible lock 'holder' preemption issues.
-*/
-
-   do {
-   while (atomic_read(&lock->val) != 0)
-   cpu_relax();
-   } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
-
-   return true;
+   return pv_virt_spin_lock(lock);
+}
+#else
+static inline bool virt_spin_lock(struct qspinlock *lock)
+{
+   return native_virt_spin_lock(lock);
 }
+#endif /* CONFIG_PARAVIRT_SPINLOCKS */
 #endif /* CONFIG_PARAVIRT */
 
 #include 
diff --git a/arch/x86/kernel/paravirt-spinlocks.c 
b/arch/x86/kernel/paravirt-spinlocks.c
index 26e4bd92f309..1be187ef8a38 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -20,6 +20,12 @@ bool pv_is_native_spin_unlock(void)
__raw_callee_save___native_queued_spin_unlock;
 }
 
+__visible bool __native_virt_spin_lock(struct qspinlock *lock)
+{
+   return native_virt_spin_lock(lock);
+}
+PV_CALLEE_SAVE_REGS_THUNK(__native_virt_spin_lock);
+
 struct pv_lock_ops pv_lock_ops = {
 #ifdef CONFIG_SMP
.queued_spin_lock_slowpath = native_queued_spin_lock_slowpath,
@@ -27,6 +33,14 @@ struct pv_lock_ops pv_lock_ops = {
.wait = paravirt_nop,
.kick = paravirt_nop,
.vcpu_is_preempted = __PV_IS_CALLEE_SAVE(_paravirt_false),
+   .virt_spin_lock = PV_CALLEE_SAVE(__native_virt_spin_lock),
 #en

Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-05 Thread Peter Zijlstra 
On Tue, Sep 05, 2017 at 03:24:43PM +0200, Juergen Gross wrote:
> diff --git a/arch/x86/include/asm/qspinlock.h 
> b/arch/x86/include/asm/qspinlock.h
> index 48a706f641f2..fbd98896385c 100644
> --- a/arch/x86/include/asm/qspinlock.h
> +++ b/arch/x86/include/asm/qspinlock.h
> @@ -17,6 +17,25 @@ static inline void native_queued_spin_unlock(struct 
> qspinlock *lock)
>   smp_store_release((u8 *)lock, 0);
>  }
>  


Should this not have:

#ifdef CONFIG_PARAVIRT

?

> +static inline bool native_virt_spin_lock(struct qspinlock *lock)
> +{
> + if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
> + return false;
> +
> + /*
> +  * On hypervisors without PARAVIRT_SPINLOCKS support we fall
> +  * back to a Test-and-Set spinlock, because fair locks have
> +  * horrible lock 'holder' preemption issues.
> +  */
> +
> + do {
> + while (atomic_read(&lock->val) != 0)
> + cpu_relax();
> + } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
> +
> + return true;
> +}

#endif

> +
>  #ifdef CONFIG_PARAVIRT_SPINLOCKS
>  extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 
> val);
>  extern void __pv_init_lock_hash(void);


>  #ifdef CONFIG_PARAVIRT
>  #define virt_spin_lock virt_spin_lock
> +#ifdef CONFIG_PARAVIRT_SPINLOCKS
>  static inline bool virt_spin_lock(struct qspinlock *lock)
>  {
> + return pv_virt_spin_lock(lock);
> +}
> +#else
> +static inline bool virt_spin_lock(struct qspinlock *lock)
> +{
> + return native_virt_spin_lock(lock);
>  }
> +#endif /* CONFIG_PARAVIRT_SPINLOCKS */
>  #endif /* CONFIG_PARAVIRT */

Because I think the above only ever uses native_virt_spin_lock() when
PARAVIRT.

> @@ -1381,6 +1382,7 @@ void __init native_smp_prepare_boot_cpu(void)
>   /* already set me in cpu_online_mask in boot_cpu_init() */
>   cpumask_set_cpu(me, cpu_callout_mask);
>   cpu_set_state_online(me);
> + native_pv_lock_init();
>  }

Aah, this is where that goes.. OK that works too.

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Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-05 Thread Juergen Gross 
On 05/09/17 15:55, Peter Zijlstra wrote:
> On Tue, Sep 05, 2017 at 03:24:43PM +0200, Juergen Gross wrote:
>> diff --git a/arch/x86/include/asm/qspinlock.h 
>> b/arch/x86/include/asm/qspinlock.h
>> index 48a706f641f2..fbd98896385c 100644
>> --- a/arch/x86/include/asm/qspinlock.h
>> +++ b/arch/x86/include/asm/qspinlock.h
>> @@ -17,6 +17,25 @@ static inline void native_queued_spin_unlock(struct 
>> qspinlock *lock)
>>  smp_store_release((u8 *)lock, 0);
>>  }
>>  
> 
> 
> Should this not have:
> 
> #ifdef CONFIG_PARAVIRT
> 
> ?

I can add it if you want.


Juergen

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Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-05 Thread Waiman Long 
On 09/05/2017 09:24 AM, Juergen Gross wrote:
> There are cases where a guest tries to switch spinlocks to bare metal
> behavior (e.g. by setting "xen_nopvspin" boot parameter). Today this
> has the downside of falling back to unfair test and set scheme for
> qspinlocks due to virt_spin_lock() detecting the virtualized
> environment.
>
> Make virt_spin_lock() a paravirt operation in order to enable users
> to select an explicit behavior like bare metal.
>
> Signed-off-by: Juergen Gross 
> ---
>  arch/x86/include/asm/paravirt.h   |  5 
>  arch/x86/include/asm/paravirt_types.h |  1 +
>  arch/x86/include/asm/qspinlock.h  | 48 
> ---
>  arch/x86/kernel/paravirt-spinlocks.c  | 14 ++
>  arch/x86/kernel/smpboot.c |  2 ++
>  5 files changed, 55 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index c25dd22f7c70..d9e954fb37df 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -725,6 +725,11 @@ static __always_inline bool pv_vcpu_is_preempted(long 
> cpu)
>   return PVOP_CALLEE1(bool, pv_lock_ops.vcpu_is_preempted, cpu);
>  }
>  
> +static __always_inline bool pv_virt_spin_lock(struct qspinlock *lock)
> +{
> + return PVOP_CALLEE1(bool, pv_lock_ops.virt_spin_lock, lock);
> +}
> +
>  #endif /* SMP && PARAVIRT_SPINLOCKS */
>  
>  #ifdef CONFIG_X86_32
> diff --git a/arch/x86/include/asm/paravirt_types.h 
> b/arch/x86/include/asm/paravirt_types.h
> index 19efefc0e27e..928f5e7953a7 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -319,6 +319,7 @@ struct pv_lock_ops {
>   void (*kick)(int cpu);
>  
>   struct paravirt_callee_save vcpu_is_preempted;
> + struct paravirt_callee_save virt_spin_lock;
>  } __no_randomize_layout;
>  
>  /* This contains all the paravirt structures: we get a convenient
> diff --git a/arch/x86/include/asm/qspinlock.h 
> b/arch/x86/include/asm/qspinlock.h
> index 48a706f641f2..fbd98896385c 100644
> --- a/arch/x86/include/asm/qspinlock.h
> +++ b/arch/x86/include/asm/qspinlock.h
> @@ -17,6 +17,25 @@ static inline void native_queued_spin_unlock(struct 
> qspinlock *lock)
>   smp_store_release((u8 *)lock, 0);
>  }
>  
> +static inline bool native_virt_spin_lock(struct qspinlock *lock)
> +{
> + if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
> + return false;
> +

I think you can take the above if statement out as you has done test in
native_pv_lock_init(). So the test will also be false here.

As this patch series is x86 specific, you should probably add "x86/" in
front of paravirt in the patch titles.

Cheers,
Longman


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Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-05 Thread Peter Zijlstra 
On Tue, Sep 05, 2017 at 10:02:57AM -0400, Waiman Long wrote:
> On 09/05/2017 09:24 AM, Juergen Gross wrote:

> > +static inline bool native_virt_spin_lock(struct qspinlock *lock)
> > +{
> > +   if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
> > +   return false;
> > +
> 
> I think you can take the above if statement out as you has done test in
> native_pv_lock_init(). So the test will also be false here.

That does mean we'll run a test-and-set spinlock until paravirt patching
happens though. I prefer to not do that.

One important point.. we must not be holding any locks when we switch
over between the two locks. Back then I spend some time making sure that
didn't happen with the X86 feature flag muck.

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Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-05 Thread Waiman Long 
On 09/05/2017 09:24 AM, Juergen Gross wrote:
> There are cases where a guest tries to switch spinlocks to bare metal
> behavior (e.g. by setting "xen_nopvspin" boot parameter). Today this
> has the downside of falling back to unfair test and set scheme for
> qspinlocks due to virt_spin_lock() detecting the virtualized
> environment.
>
> Make virt_spin_lock() a paravirt operation in order to enable users
> to select an explicit behavior like bare metal.
>
> Signed-off-by: Juergen Gross 
> ---
>  arch/x86/include/asm/paravirt.h   |  5 
>  arch/x86/include/asm/paravirt_types.h |  1 +
>  arch/x86/include/asm/qspinlock.h  | 48 
> ---
>  arch/x86/kernel/paravirt-spinlocks.c  | 14 ++
>  arch/x86/kernel/smpboot.c |  2 ++
>  5 files changed, 55 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index c25dd22f7c70..d9e954fb37df 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -725,6 +725,11 @@ static __always_inline bool pv_vcpu_is_preempted(long 
> cpu)
>   return PVOP_CALLEE1(bool, pv_lock_ops.vcpu_is_preempted, cpu);
>  }
>  
> +static __always_inline bool pv_virt_spin_lock(struct qspinlock *lock)
> +{
> + return PVOP_CALLEE1(bool, pv_lock_ops.virt_spin_lock, lock);
> +}
> +
>  #endif /* SMP && PARAVIRT_SPINLOCKS */
>  
>  #ifdef CONFIG_X86_32
> diff --git a/arch/x86/include/asm/paravirt_types.h 
> b/arch/x86/include/asm/paravirt_types.h
> index 19efefc0e27e..928f5e7953a7 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -319,6 +319,7 @@ struct pv_lock_ops {
>   void (*kick)(int cpu);
>  
>   struct paravirt_callee_save vcpu_is_preempted;
> + struct paravirt_callee_save virt_spin_lock;
>  } __no_randomize_layout;
>  
>  /* This contains all the paravirt structures: we get a convenient
> diff --git a/arch/x86/include/asm/qspinlock.h 
> b/arch/x86/include/asm/qspinlock.h
> index 48a706f641f2..fbd98896385c 100644
> --- a/arch/x86/include/asm/qspinlock.h
> +++ b/arch/x86/include/asm/qspinlock.h
> @@ -17,6 +17,25 @@ static inline void native_queued_spin_unlock(struct 
> qspinlock *lock)
>   smp_store_release((u8 *)lock, 0);
>  }
>  
> +static inline bool native_virt_spin_lock(struct qspinlock *lock)
> +{
> + if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
> + return false;
> +
> + /*
> +  * On hypervisors without PARAVIRT_SPINLOCKS support we fall
> +  * back to a Test-and-Set spinlock, because fair locks have
> +  * horrible lock 'holder' preemption issues.
> +  */
> +
> + do {
> + while (atomic_read(&lock->val) != 0)
> + cpu_relax();
> + } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
> +
> + return true;
> +}
> +
>  #ifdef CONFIG_PARAVIRT_SPINLOCKS
>  extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 
> val);
>  extern void __pv_init_lock_hash(void);
> @@ -38,33 +57,32 @@ static inline bool vcpu_is_preempted(long cpu)
>  {
>   return pv_vcpu_is_preempted(cpu);
>  }
> +
> +void native_pv_lock_init(void) __init;
>  #else
>  static inline void queued_spin_unlock(struct qspinlock *lock)
>  {
>   native_queued_spin_unlock(lock);
>  }
> +
> +static inline void native_pv_lock_init(void)
> +{
> +}
>  #endif
>  
>  #ifdef CONFIG_PARAVIRT
>  #define virt_spin_lock virt_spin_lock
> +#ifdef CONFIG_PARAVIRT_SPINLOCKS
>  static inline bool virt_spin_lock(struct qspinlock *lock)
>  {
> - if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
> - return false;

Have you consider just add one more jump label here to skip
virt_spin_lock when KVM or Xen want to do so?

> -
> - /*
> -  * On hypervisors without PARAVIRT_SPINLOCKS support we fall
> -  * back to a Test-and-Set spinlock, because fair locks have
> -  * horrible lock 'holder' preemption issues.
> -  */
> -
> - do {
> - while (atomic_read(&lock->val) != 0)
> - cpu_relax();
> - } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
> -
> - return true;
> + return pv_virt_spin_lock(lock);
> +}
> +#else
> +static inline bool virt_spin_lock(struct qspinlock *lock)
> +{
> + return native_virt_spin_lock(lock);
>  }
> +#endif /* CONFIG_PARAVIRT_SPINLOCKS */
>  #endif /* CONFIG_PARAVIRT */
>  
>  #include 
> diff --git a/arch/x86/kernel/paravirt-spinlocks.c 
> b/arch/x86/kernel/paravirt-spinlocks.c
> index 26e4bd92f309..1be187ef8a38 100644
> --- a/arch/x86/kernel/paravirt-spinlocks.c
> +++ b/arch/x86/kernel/paravirt-spinlocks.c
> @@ -20,6 +20,12 @@ bool pv_is_native_spin_unlock(void)
>   __raw_callee_save___native_queued_spin_unlock;
>  }
>  
> +__visible bool __native_virt_spin_lock(struct qspinlock *lock)
> +{
> + return native_virt_spin_lock(lock);
> +}
> +PV_CALLEE_SAVE_REGS_THUNK(__native_virt_spin_lock);

I have so

Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-05 Thread Juergen Gross 
On 05/09/17 16:10, Waiman Long wrote:
> On 09/05/2017 09:24 AM, Juergen Gross wrote:
>> There are cases where a guest tries to switch spinlocks to bare metal
>> behavior (e.g. by setting "xen_nopvspin" boot parameter). Today this
>> has the downside of falling back to unfair test and set scheme for
>> qspinlocks due to virt_spin_lock() detecting the virtualized
>> environment.
>>
>> Make virt_spin_lock() a paravirt operation in order to enable users
>> to select an explicit behavior like bare metal.
>>
>> Signed-off-by: Juergen Gross 
>> ---
>>  arch/x86/include/asm/paravirt.h   |  5 
>>  arch/x86/include/asm/paravirt_types.h |  1 +
>>  arch/x86/include/asm/qspinlock.h  | 48 
>> ---
>>  arch/x86/kernel/paravirt-spinlocks.c  | 14 ++
>>  arch/x86/kernel/smpboot.c |  2 ++
>>  5 files changed, 55 insertions(+), 15 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/paravirt.h 
>> b/arch/x86/include/asm/paravirt.h
>> index c25dd22f7c70..d9e954fb37df 100644
>> --- a/arch/x86/include/asm/paravirt.h
>> +++ b/arch/x86/include/asm/paravirt.h
>> @@ -725,6 +725,11 @@ static __always_inline bool pv_vcpu_is_preempted(long 
>> cpu)
>>  return PVOP_CALLEE1(bool, pv_lock_ops.vcpu_is_preempted, cpu);
>>  }
>>  
>> +static __always_inline bool pv_virt_spin_lock(struct qspinlock *lock)
>> +{
>> +return PVOP_CALLEE1(bool, pv_lock_ops.virt_spin_lock, lock);
>> +}
>> +
>>  #endif /* SMP && PARAVIRT_SPINLOCKS */
>>  
>>  #ifdef CONFIG_X86_32
>> diff --git a/arch/x86/include/asm/paravirt_types.h 
>> b/arch/x86/include/asm/paravirt_types.h
>> index 19efefc0e27e..928f5e7953a7 100644
>> --- a/arch/x86/include/asm/paravirt_types.h
>> +++ b/arch/x86/include/asm/paravirt_types.h
>> @@ -319,6 +319,7 @@ struct pv_lock_ops {
>>  void (*kick)(int cpu);
>>  
>>  struct paravirt_callee_save vcpu_is_preempted;
>> +struct paravirt_callee_save virt_spin_lock;
>>  } __no_randomize_layout;
>>  
>>  /* This contains all the paravirt structures: we get a convenient
>> diff --git a/arch/x86/include/asm/qspinlock.h 
>> b/arch/x86/include/asm/qspinlock.h
>> index 48a706f641f2..fbd98896385c 100644
>> --- a/arch/x86/include/asm/qspinlock.h
>> +++ b/arch/x86/include/asm/qspinlock.h
>> @@ -17,6 +17,25 @@ static inline void native_queued_spin_unlock(struct 
>> qspinlock *lock)
>>  smp_store_release((u8 *)lock, 0);
>>  }
>>  
>> +static inline bool native_virt_spin_lock(struct qspinlock *lock)
>> +{
>> +if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
>> +return false;
>> +
>> +/*
>> + * On hypervisors without PARAVIRT_SPINLOCKS support we fall
>> + * back to a Test-and-Set spinlock, because fair locks have
>> + * horrible lock 'holder' preemption issues.
>> + */
>> +
>> +do {
>> +while (atomic_read(&lock->val) != 0)
>> +cpu_relax();
>> +} while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
>> +
>> +return true;
>> +}
>> +
>>  #ifdef CONFIG_PARAVIRT_SPINLOCKS
>>  extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 
>> val);
>>  extern void __pv_init_lock_hash(void);
>> @@ -38,33 +57,32 @@ static inline bool vcpu_is_preempted(long cpu)
>>  {
>>  return pv_vcpu_is_preempted(cpu);
>>  }
>> +
>> +void native_pv_lock_init(void) __init;
>>  #else
>>  static inline void queued_spin_unlock(struct qspinlock *lock)
>>  {
>>  native_queued_spin_unlock(lock);
>>  }
>> +
>> +static inline void native_pv_lock_init(void)
>> +{
>> +}
>>  #endif
>>  
>>  #ifdef CONFIG_PARAVIRT
>>  #define virt_spin_lock virt_spin_lock
>> +#ifdef CONFIG_PARAVIRT_SPINLOCKS
>>  static inline bool virt_spin_lock(struct qspinlock *lock)
>>  {
>> -if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
>> -return false;
> 
> Have you consider just add one more jump label here to skip
> virt_spin_lock when KVM or Xen want to do so?

Why? Did you look at patch 4? This is the way to do it...

> 
>> -
>> -/*
>> - * On hypervisors without PARAVIRT_SPINLOCKS support we fall
>> - * back to a Test-and-Set spinlock, because fair locks have
>> - * horrible lock 'holder' preemption issues.
>> - */
>> -
>> -do {
>> -while (atomic_read(&lock->val) != 0)
>> -cpu_relax();
>> -} while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
>> -
>> -return true;
>> +return pv_virt_spin_lock(lock);
>> +}
>> +#else
>> +static inline bool virt_spin_lock(struct qspinlock *lock)
>> +{
>> +return native_virt_spin_lock(lock);
>>  }
>> +#endif /* CONFIG_PARAVIRT_SPINLOCKS */
>>  #endif /* CONFIG_PARAVIRT */
>>  
>>  #include 
>> diff --git a/arch/x86/kernel/paravirt-spinlocks.c 
>> b/arch/x86/kernel/paravirt-spinlocks.c
>> index 26e4bd92f309..1be187ef8a38 100644
>> --- a/arch/x86/kernel/paravirt-spinlocks.c
>> +++ b/arch/x86/kernel/paravirt-spinlocks.c
>> @@ -20,6 +20,12 @@ bool pv_is_native_spin_unlock(void)
>>  __raw_callee_save___native_

Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-05 Thread Waiman Long 
On 09/05/2017 10:08 AM, Peter Zijlstra wrote:
> On Tue, Sep 05, 2017 at 10:02:57AM -0400, Waiman Long wrote:
>> On 09/05/2017 09:24 AM, Juergen Gross wrote:
>>> +static inline bool native_virt_spin_lock(struct qspinlock *lock)
>>> +{
>>> +   if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
>>> +   return false;
>>> +
>> I think you can take the above if statement out as you has done test in
>> native_pv_lock_init(). So the test will also be false here.
> That does mean we'll run a test-and-set spinlock until paravirt patching
> happens though. I prefer to not do that.
>
> One important point.. we must not be holding any locks when we switch
> over between the two locks. Back then I spend some time making sure that
> didn't happen with the X86 feature flag muck.

AFAICT, native_pv_lock_init() is called before SMP init. So it shouldn't
matter.

Cheers,
Longman


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Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-05 Thread Waiman Long 
On 09/05/2017 10:18 AM, Juergen Gross wrote:
> On 05/09/17 16:10, Waiman Long wrote:
>> On 09/05/2017 09:24 AM, Juergen Gross wrote:
>>> There are cases where a guest tries to switch spinlocks to bare metal
>>> behavior (e.g. by setting "xen_nopvspin" boot parameter). Today this
>>> has the downside of falling back to unfair test and set scheme for
>>> qspinlocks due to virt_spin_lock() detecting the virtualized
>>> environment.
>>>
>>> Make virt_spin_lock() a paravirt operation in order to enable users
>>> to select an explicit behavior like bare metal.
>>>
>>> Signed-off-by: Juergen Gross 
>>> ---
>>>  arch/x86/include/asm/paravirt.h   |  5 
>>>  arch/x86/include/asm/paravirt_types.h |  1 +
>>>  arch/x86/include/asm/qspinlock.h  | 48 
>>> ---
>>>  arch/x86/kernel/paravirt-spinlocks.c  | 14 ++
>>>  arch/x86/kernel/smpboot.c |  2 ++
>>>  5 files changed, 55 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/arch/x86/include/asm/paravirt.h 
>>> b/arch/x86/include/asm/paravirt.h
>>> index c25dd22f7c70..d9e954fb37df 100644
>>> --- a/arch/x86/include/asm/paravirt.h
>>> +++ b/arch/x86/include/asm/paravirt.h
>>> @@ -725,6 +725,11 @@ static __always_inline bool pv_vcpu_is_preempted(long 
>>> cpu)
>>> return PVOP_CALLEE1(bool, pv_lock_ops.vcpu_is_preempted, cpu);
>>>  }
>>>  
>>> +static __always_inline bool pv_virt_spin_lock(struct qspinlock *lock)
>>> +{
>>> +   return PVOP_CALLEE1(bool, pv_lock_ops.virt_spin_lock, lock);
>>> +}
>>> +
>>>  #endif /* SMP && PARAVIRT_SPINLOCKS */
>>>  
>>>  #ifdef CONFIG_X86_32
>>> diff --git a/arch/x86/include/asm/paravirt_types.h 
>>> b/arch/x86/include/asm/paravirt_types.h
>>> index 19efefc0e27e..928f5e7953a7 100644
>>> --- a/arch/x86/include/asm/paravirt_types.h
>>> +++ b/arch/x86/include/asm/paravirt_types.h
>>> @@ -319,6 +319,7 @@ struct pv_lock_ops {
>>> void (*kick)(int cpu);
>>>  
>>> struct paravirt_callee_save vcpu_is_preempted;
>>> +   struct paravirt_callee_save virt_spin_lock;
>>>  } __no_randomize_layout;
>>>  
>>>  /* This contains all the paravirt structures: we get a convenient
>>> diff --git a/arch/x86/include/asm/qspinlock.h 
>>> b/arch/x86/include/asm/qspinlock.h
>>> index 48a706f641f2..fbd98896385c 100644
>>> --- a/arch/x86/include/asm/qspinlock.h
>>> +++ b/arch/x86/include/asm/qspinlock.h
>>> @@ -17,6 +17,25 @@ static inline void native_queued_spin_unlock(struct 
>>> qspinlock *lock)
>>> smp_store_release((u8 *)lock, 0);
>>>  }
>>>  
>>> +static inline bool native_virt_spin_lock(struct qspinlock *lock)
>>> +{
>>> +   if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
>>> +   return false;
>>> +
>>> +   /*
>>> +* On hypervisors without PARAVIRT_SPINLOCKS support we fall
>>> +* back to a Test-and-Set spinlock, because fair locks have
>>> +* horrible lock 'holder' preemption issues.
>>> +*/
>>> +
>>> +   do {
>>> +   while (atomic_read(&lock->val) != 0)
>>> +   cpu_relax();
>>> +   } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
>>> +
>>> +   return true;
>>> +}
>>> +
>>>  #ifdef CONFIG_PARAVIRT_SPINLOCKS
>>>  extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 
>>> val);
>>>  extern void __pv_init_lock_hash(void);
>>> @@ -38,33 +57,32 @@ static inline bool vcpu_is_preempted(long cpu)
>>>  {
>>> return pv_vcpu_is_preempted(cpu);
>>>  }
>>> +
>>> +void native_pv_lock_init(void) __init;
>>>  #else
>>>  static inline void queued_spin_unlock(struct qspinlock *lock)
>>>  {
>>> native_queued_spin_unlock(lock);
>>>  }
>>> +
>>> +static inline void native_pv_lock_init(void)
>>> +{
>>> +}
>>>  #endif
>>>  
>>>  #ifdef CONFIG_PARAVIRT
>>>  #define virt_spin_lock virt_spin_lock
>>> +#ifdef CONFIG_PARAVIRT_SPINLOCKS
>>>  static inline bool virt_spin_lock(struct qspinlock *lock)
>>>  {
>>> -   if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
>>> -   return false;
>> Have you consider just add one more jump label here to skip
>> virt_spin_lock when KVM or Xen want to do so?
> Why? Did you look at patch 4? This is the way to do it...

I asked this because of my performance concern as stated later in the email.

>>> -
>>> -   /*
>>> -* On hypervisors without PARAVIRT_SPINLOCKS support we fall
>>> -* back to a Test-and-Set spinlock, because fair locks have
>>> -* horrible lock 'holder' preemption issues.
>>> -*/
>>> -
>>> -   do {
>>> -   while (atomic_read(&lock->val) != 0)
>>> -   cpu_relax();
>>> -   } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
>>> -
>>> -   return true;
>>> +   return pv_virt_spin_lock(lock);
>>> +}
>>> +#else
>>> +static inline bool virt_spin_lock(struct qspinlock *lock)
>>> +{
>>> +   return native_virt_spin_lock(lock);
>>>  }
>>> +#endif /* CONFIG_PARAVIRT_SPINLOCKS */
>>>  #endif /* CONFIG_PARAVIRT */
>>>  
>>>  #include 
>>> diff --git a/arch/x86/kernel/paravirt-spinlocks.c 
>>> b/arch/x86/kernel/paravirt-spinlocks.c
>>> index 26e4

Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-05 Thread Waiman Long 
On 09/05/2017 10:24 AM, Waiman Long wrote:
> On 09/05/2017 10:18 AM, Juergen Gross wrote:
>> On 05/09/17 16:10, Waiman Long wrote:
>>> On 09/05/2017 09:24 AM, Juergen Gross wrote:
 There are cases where a guest tries to switch spinlocks to bare metal
 behavior (e.g. by setting "xen_nopvspin" boot parameter). Today this
 has the downside of falling back to unfair test and set scheme for
 qspinlocks due to virt_spin_lock() detecting the virtualized
 environment.

 Make virt_spin_lock() a paravirt operation in order to enable users
 to select an explicit behavior like bare metal.

 Signed-off-by: Juergen Gross 
 ---
  arch/x86/include/asm/paravirt.h   |  5 
  arch/x86/include/asm/paravirt_types.h |  1 +
  arch/x86/include/asm/qspinlock.h  | 48 
 ---
  arch/x86/kernel/paravirt-spinlocks.c  | 14 ++
  arch/x86/kernel/smpboot.c |  2 ++
  5 files changed, 55 insertions(+), 15 deletions(-)

 diff --git a/arch/x86/include/asm/paravirt.h 
 b/arch/x86/include/asm/paravirt.h
 index c25dd22f7c70..d9e954fb37df 100644
 --- a/arch/x86/include/asm/paravirt.h
 +++ b/arch/x86/include/asm/paravirt.h
 @@ -725,6 +725,11 @@ static __always_inline bool pv_vcpu_is_preempted(long 
 cpu)
return PVOP_CALLEE1(bool, pv_lock_ops.vcpu_is_preempted, cpu);
  }
  
 +static __always_inline bool pv_virt_spin_lock(struct qspinlock *lock)
 +{
 +  return PVOP_CALLEE1(bool, pv_lock_ops.virt_spin_lock, lock);
 +}
 +
  #endif /* SMP && PARAVIRT_SPINLOCKS */
  
  #ifdef CONFIG_X86_32
 diff --git a/arch/x86/include/asm/paravirt_types.h 
 b/arch/x86/include/asm/paravirt_types.h
 index 19efefc0e27e..928f5e7953a7 100644
 --- a/arch/x86/include/asm/paravirt_types.h
 +++ b/arch/x86/include/asm/paravirt_types.h
 @@ -319,6 +319,7 @@ struct pv_lock_ops {
void (*kick)(int cpu);
  
struct paravirt_callee_save vcpu_is_preempted;
 +  struct paravirt_callee_save virt_spin_lock;
  } __no_randomize_layout;
  
  /* This contains all the paravirt structures: we get a convenient
 diff --git a/arch/x86/include/asm/qspinlock.h 
 b/arch/x86/include/asm/qspinlock.h
 index 48a706f641f2..fbd98896385c 100644
 --- a/arch/x86/include/asm/qspinlock.h
 +++ b/arch/x86/include/asm/qspinlock.h
 @@ -17,6 +17,25 @@ static inline void native_queued_spin_unlock(struct 
 qspinlock *lock)
smp_store_release((u8 *)lock, 0);
  }
  
 +static inline bool native_virt_spin_lock(struct qspinlock *lock)
 +{
 +  if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
 +  return false;
 +
 +  /*
 +   * On hypervisors without PARAVIRT_SPINLOCKS support we fall
 +   * back to a Test-and-Set spinlock, because fair locks have
 +   * horrible lock 'holder' preemption issues.
 +   */
 +
 +  do {
 +  while (atomic_read(&lock->val) != 0)
 +  cpu_relax();
 +  } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
 +
 +  return true;
 +}
 +
  #ifdef CONFIG_PARAVIRT_SPINLOCKS
  extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 
 val);
  extern void __pv_init_lock_hash(void);
 @@ -38,33 +57,32 @@ static inline bool vcpu_is_preempted(long cpu)
  {
return pv_vcpu_is_preempted(cpu);
  }
 +
 +void native_pv_lock_init(void) __init;
  #else
  static inline void queued_spin_unlock(struct qspinlock *lock)
  {
native_queued_spin_unlock(lock);
  }
 +
 +static inline void native_pv_lock_init(void)
 +{
 +}
  #endif
  
  #ifdef CONFIG_PARAVIRT
  #define virt_spin_lock virt_spin_lock
 +#ifdef CONFIG_PARAVIRT_SPINLOCKS
  static inline bool virt_spin_lock(struct qspinlock *lock)
  {
 -  if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
 -  return false;
>>> Have you consider just add one more jump label here to skip
>>> virt_spin_lock when KVM or Xen want to do so?
>> Why? Did you look at patch 4? This is the way to do it...
> I asked this because of my performance concern as stated later in the email.

For clarification, I was actually asking if you consider just adding one
more jump label to skip it for Xen/KVM instead of making
virt_spin_lock() a pv-op.

Cheers,
Longman

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Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-05 Thread Juergen Gross 
On 05/09/17 16:31, Waiman Long wrote:
> On 09/05/2017 10:24 AM, Waiman Long wrote:
>> On 09/05/2017 10:18 AM, Juergen Gross wrote:
>>> On 05/09/17 16:10, Waiman Long wrote:
 On 09/05/2017 09:24 AM, Juergen Gross wrote:
> There are cases where a guest tries to switch spinlocks to bare metal
> behavior (e.g. by setting "xen_nopvspin" boot parameter). Today this
> has the downside of falling back to unfair test and set scheme for
> qspinlocks due to virt_spin_lock() detecting the virtualized
> environment.
>
> Make virt_spin_lock() a paravirt operation in order to enable users
> to select an explicit behavior like bare metal.
>
> Signed-off-by: Juergen Gross 
> ---
>  arch/x86/include/asm/paravirt.h   |  5 
>  arch/x86/include/asm/paravirt_types.h |  1 +
>  arch/x86/include/asm/qspinlock.h  | 48 
> ---
>  arch/x86/kernel/paravirt-spinlocks.c  | 14 ++
>  arch/x86/kernel/smpboot.c |  2 ++
>  5 files changed, 55 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/include/asm/paravirt.h 
> b/arch/x86/include/asm/paravirt.h
> index c25dd22f7c70..d9e954fb37df 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -725,6 +725,11 @@ static __always_inline bool 
> pv_vcpu_is_preempted(long cpu)
>   return PVOP_CALLEE1(bool, pv_lock_ops.vcpu_is_preempted, cpu);
>  }
>  
> +static __always_inline bool pv_virt_spin_lock(struct qspinlock *lock)
> +{
> + return PVOP_CALLEE1(bool, pv_lock_ops.virt_spin_lock, lock);
> +}
> +
>  #endif /* SMP && PARAVIRT_SPINLOCKS */
>  
>  #ifdef CONFIG_X86_32
> diff --git a/arch/x86/include/asm/paravirt_types.h 
> b/arch/x86/include/asm/paravirt_types.h
> index 19efefc0e27e..928f5e7953a7 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -319,6 +319,7 @@ struct pv_lock_ops {
>   void (*kick)(int cpu);
>  
>   struct paravirt_callee_save vcpu_is_preempted;
> + struct paravirt_callee_save virt_spin_lock;
>  } __no_randomize_layout;
>  
>  /* This contains all the paravirt structures: we get a convenient
> diff --git a/arch/x86/include/asm/qspinlock.h 
> b/arch/x86/include/asm/qspinlock.h
> index 48a706f641f2..fbd98896385c 100644
> --- a/arch/x86/include/asm/qspinlock.h
> +++ b/arch/x86/include/asm/qspinlock.h
> @@ -17,6 +17,25 @@ static inline void native_queued_spin_unlock(struct 
> qspinlock *lock)
>   smp_store_release((u8 *)lock, 0);
>  }
>  
> +static inline bool native_virt_spin_lock(struct qspinlock *lock)
> +{
> + if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
> + return false;
> +
> + /*
> +  * On hypervisors without PARAVIRT_SPINLOCKS support we fall
> +  * back to a Test-and-Set spinlock, because fair locks have
> +  * horrible lock 'holder' preemption issues.
> +  */
> +
> + do {
> + while (atomic_read(&lock->val) != 0)
> + cpu_relax();
> + } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
> +
> + return true;
> +}
> +
>  #ifdef CONFIG_PARAVIRT_SPINLOCKS
>  extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 
> val);
>  extern void __pv_init_lock_hash(void);
> @@ -38,33 +57,32 @@ static inline bool vcpu_is_preempted(long cpu)
>  {
>   return pv_vcpu_is_preempted(cpu);
>  }
> +
> +void native_pv_lock_init(void) __init;
>  #else
>  static inline void queued_spin_unlock(struct qspinlock *lock)
>  {
>   native_queued_spin_unlock(lock);
>  }
> +
> +static inline void native_pv_lock_init(void)
> +{
> +}
>  #endif
>  
>  #ifdef CONFIG_PARAVIRT
>  #define virt_spin_lock virt_spin_lock
> +#ifdef CONFIG_PARAVIRT_SPINLOCKS
>  static inline bool virt_spin_lock(struct qspinlock *lock)
>  {
> - if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
> - return false;
 Have you consider just add one more jump label here to skip
 virt_spin_lock when KVM or Xen want to do so?
>>> Why? Did you look at patch 4? This is the way to do it...
>> I asked this because of my performance concern as stated later in the email.
> 
> For clarification, I was actually asking if you consider just adding one
> more jump label to skip it for Xen/KVM instead of making
> virt_spin_lock() a pv-op.

Aah, okay.

Bare metal could make use of this jump label, too.

I'll have a try how it looks like.


Juergen


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Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-06 Thread Peter Zijlstra 

Guys, please trim email.

On Tue, Sep 05, 2017 at 10:31:46AM -0400, Waiman Long wrote:
> For clarification, I was actually asking if you consider just adding one
> more jump label to skip it for Xen/KVM instead of making
> virt_spin_lock() a pv-op.

I don't understand. What performance are you worried about. Native will
now do: "xor rax,rax; jnz some_cold_label" that's fairly trival code.

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Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-06 Thread Waiman Long 
On 09/06/2017 03:08 AM, Peter Zijlstra wrote:
> Guys, please trim email.
>
> On Tue, Sep 05, 2017 at 10:31:46AM -0400, Waiman Long wrote:
>> For clarification, I was actually asking if you consider just adding one
>> more jump label to skip it for Xen/KVM instead of making
>> virt_spin_lock() a pv-op.
> I don't understand. What performance are you worried about. Native will
> now do: "xor rax,rax; jnz some_cold_label" that's fairly trival code.

It is not native that I am talking about. I am worry about VM with
non-Xen/KVM hypervisor where virt_spin_lock() will actually be called.
Now that function will become a callee-saved function call instead of
being inlined into the native slowpath function.

Cheers,
Longman


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Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-06 Thread Peter Zijlstra 
On Wed, Sep 06, 2017 at 08:44:09AM -0400, Waiman Long wrote:
> On 09/06/2017 03:08 AM, Peter Zijlstra wrote:
> > Guys, please trim email.
> >
> > On Tue, Sep 05, 2017 at 10:31:46AM -0400, Waiman Long wrote:
> >> For clarification, I was actually asking if you consider just adding one
> >> more jump label to skip it for Xen/KVM instead of making
> >> virt_spin_lock() a pv-op.
> > I don't understand. What performance are you worried about. Native will
> > now do: "xor rax,rax; jnz some_cold_label" that's fairly trival code.
> 
> It is not native that I am talking about. I am worry about VM with
> non-Xen/KVM hypervisor where virt_spin_lock() will actually be called.
> Now that function will become a callee-saved function call instead of
> being inlined into the native slowpath function.

But only if we actually end up using the test-and-set thing, because if
you have paravirt we end up using that.

And the test-and-set thing sucks anyway. But yes, you're right, that
case gets worse.

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Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

2017-09-06 Thread Waiman Long 
On 09/06/2017 09:06 AM, Peter Zijlstra wrote:
> On Wed, Sep 06, 2017 at 08:44:09AM -0400, Waiman Long wrote:
>> On 09/06/2017 03:08 AM, Peter Zijlstra wrote:
>>> Guys, please trim email.
>>>
>>> On Tue, Sep 05, 2017 at 10:31:46AM -0400, Waiman Long wrote:
 For clarification, I was actually asking if you consider just adding one
 more jump label to skip it for Xen/KVM instead of making
 virt_spin_lock() a pv-op.
>>> I don't understand. What performance are you worried about. Native will
>>> now do: "xor rax,rax; jnz some_cold_label" that's fairly trival code.
>> It is not native that I am talking about. I am worry about VM with
>> non-Xen/KVM hypervisor where virt_spin_lock() will actually be called.
>> Now that function will become a callee-saved function call instead of
>> being inlined into the native slowpath function.
> But only if we actually end up using the test-and-set thing, because if
> you have paravirt we end up using that.

I am talking about scenario like a kernel with paravirt spinlock running
in a VM managed by VMware, for example. We may not want to penalize them
while there are alternatives with less penalty.

Cheers,
Longman

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