linux-kernel - Re: [PATCH 6/8] powerpc/pseries: implement paravirt qspinlocks for SPLPAR

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Date:   Thu, 2 Jul 2020 17:01:06 -0400
From:   Waiman Long <longman@...hat.com>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        Anton Blanchard <anton@...abs.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm-ppc@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH 6/8] powerpc/pseries: implement paravirt qspinlocks for
 SPLPAR

On 7/2/20 3:48 AM, Nicholas Piggin wrote:
> Signed-off-by: Nicholas Piggin <npiggin@...il.com>
> ---
>   arch/powerpc/include/asm/paravirt.h           | 23 ++++++++
>   arch/powerpc/include/asm/qspinlock.h          | 55 +++++++++++++++++++
>   arch/powerpc/include/asm/qspinlock_paravirt.h |  5 ++
>   arch/powerpc/platforms/pseries/Kconfig        |  5 ++
>   arch/powerpc/platforms/pseries/setup.c        |  6 +-
>   include/asm-generic/qspinlock.h               |  2 +
>   6 files changed, 95 insertions(+), 1 deletion(-)
>   create mode 100644 arch/powerpc/include/asm/qspinlock_paravirt.h
>
> diff --git a/arch/powerpc/include/asm/paravirt.h b/arch/powerpc/include/asm/paravirt.h
> index 7a8546660a63..5fae9dfa6fe9 100644
> --- a/arch/powerpc/include/asm/paravirt.h
> +++ b/arch/powerpc/include/asm/paravirt.h
> @@ -29,6 +29,16 @@ static inline void yield_to_preempted(int cpu, u32 yield_count)
>   {
>   	plpar_hcall_norets(H_CONFER, get_hard_smp_processor_id(cpu), yield_count);
>   }
> +
> +static inline void prod_cpu(int cpu)
> +{
> +	plpar_hcall_norets(H_PROD, get_hard_smp_processor_id(cpu));
> +}
> +
> +static inline void yield_to_any(void)
> +{
> +	plpar_hcall_norets(H_CONFER, -1, 0);
> +}
>   #else
>   static inline bool is_shared_processor(void)
>   {
> @@ -45,6 +55,19 @@ static inline void yield_to_preempted(int cpu, u32 yield_count)
>   {
>   	___bad_yield_to_preempted(); /* This would be a bug */
>   }
> +
> +extern void ___bad_yield_to_any(void);
> +static inline void yield_to_any(void)
> +{
> +	___bad_yield_to_any(); /* This would be a bug */
> +}
> +
> +extern void ___bad_prod_cpu(void);
> +static inline void prod_cpu(int cpu)
> +{
> +	___bad_prod_cpu(); /* This would be a bug */
> +}
> +
>   #endif
>   
>   #define vcpu_is_preempted vcpu_is_preempted
> diff --git a/arch/powerpc/include/asm/qspinlock.h b/arch/powerpc/include/asm/qspinlock.h
> index f84da77b6bb7..997a9a32df77 100644
> --- a/arch/powerpc/include/asm/qspinlock.h
> +++ b/arch/powerpc/include/asm/qspinlock.h
> @@ -3,9 +3,36 @@
>   #define _ASM_POWERPC_QSPINLOCK_H
>   
>   #include <asm-generic/qspinlock_types.h>
> +#include <asm/paravirt.h>
>   
>   #define _Q_PENDING_LOOPS	(1 << 9) /* not tuned */
>   
> +#ifdef CONFIG_PARAVIRT_SPINLOCKS
> +extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
> +extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
> +
> +static __always_inline void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
> +{
> +	if (!is_shared_processor())
> +		native_queued_spin_lock_slowpath(lock, val);
> +	else
> +		__pv_queued_spin_lock_slowpath(lock, val);
> +}

You may need to match the use of __pv_queued_spin_lock_slowpath() with 
the corresponding __pv_queued_spin_unlock(), e.g.

#define queued_spin_unlock queued_spin_unlock
static inline queued_spin_unlock(struct qspinlock *lock)
{
         if (!is_shared_processor())
                 smp_store_release(&lock->locked, 0);
         else
                 __pv_queued_spin_unlock(lock);
}

Otherwise, pv_kick() will never be called.

Cheers,
Longman