Re: [PATCH v2 1/1] s390/spinlock: Provide vcpu_is_preempted

[Christian Borntraeger]

On 09/29/2016 05:51 PM, Christian Borntraeger wrote:
> this implements the s390 backend for commit
> "kernel/sched: introduce vcpu preempted check interface"
> by reworking the existing smp_vcpu_scheduled into
> arch_vcpu_is_preempted. We can then also get rid of the
> local cpu_is_preempted function by moving the
> CIF_ENABLED_WAIT test into arch_vcpu_is_preempted.
> 
> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>


Martin, Peter,

I think we could go with the patch as is. In other words not providing
arch_vcpu_is_preempted for !CONFIG_SMP.

This will result in compile errors if code does spinning or yielding for
non-SMP kernels - which does not make sense to me, so this might actually
be a nice indicator.
If you prefer the !CONFIG_SMP implementation let me know and I will respin.

In any case, Martin if the patch is ok for you, can you ack, so that Peter 
can take that patch together with Pan Xinhui series?

> ---
>  arch/s390/include/asm/spinlock.h |  3 +++
>  arch/s390/kernel/smp.c           |  9 +++++++--
>  arch/s390/lib/spinlock.c         | 25 ++++++++-----------------
>  3 files changed, 18 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/s390/include/asm/spinlock.h b/arch/s390/include/asm/spinlock.h
> index 63ebf37..e16e02f 100644
> --- a/arch/s390/include/asm/spinlock.h
> +++ b/arch/s390/include/asm/spinlock.h
> @@ -21,6 +21,9 @@ _raw_compare_and_swap(unsigned int *lock, unsigned int old, unsigned int new)
>  	return __sync_bool_compare_and_swap(lock, old, new);
>  }
> 
> +bool arch_vcpu_is_preempted(int cpu);
> +#define vcpu_is_preempted arch_vcpu_is_preempted
> +
>  /*
>   * Simple spin lock operations.  There are two variants, one clears IRQ's
>   * on the local processor, one does not.
> diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
> index 7b89a75..4aadd16 100644
> --- a/arch/s390/kernel/smp.c
> +++ b/arch/s390/kernel/smp.c
> @@ -376,10 +376,15 @@ int smp_find_processor_id(u16 address)
>  	return -1;
>  }
> 
> -int smp_vcpu_scheduled(int cpu)
> +bool arch_vcpu_is_preempted(int cpu)
>  {
> -	return pcpu_running(pcpu_devices + cpu);
> +	if (test_cpu_flag_of(CIF_ENABLED_WAIT, cpu))
> +		return false;
> +	if (pcpu_running(pcpu_devices + cpu))
> +		return false;
> +	return true;
>  }
> +EXPORT_SYMBOL(arch_vcpu_is_preempted);
> 
>  void smp_yield_cpu(int cpu)
>  {
> diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c
> index e5f50a7..e48a48e 100644
> --- a/arch/s390/lib/spinlock.c
> +++ b/arch/s390/lib/spinlock.c
> @@ -37,15 +37,6 @@ static inline void _raw_compare_and_delay(unsigned int *lock, unsigned int old)
>  	asm(".insn rsy,0xeb0000000022,%0,0,%1" : : "d" (old), "Q" (*lock));
>  }
> 
> -static inline int cpu_is_preempted(int cpu)
> -{
> -	if (test_cpu_flag_of(CIF_ENABLED_WAIT, cpu))
> -		return 0;
> -	if (smp_vcpu_scheduled(cpu))
> -		return 0;
> -	return 1;
> -}
> -
>  void arch_spin_lock_wait(arch_spinlock_t *lp)
>  {
>  	unsigned int cpu = SPINLOCK_LOCKVAL;
> @@ -62,7 +53,7 @@ void arch_spin_lock_wait(arch_spinlock_t *lp)
>  			continue;
>  		}
>  		/* First iteration: check if the lock owner is running. */
> -		if (first_diag && cpu_is_preempted(~owner)) {
> +		if (first_diag && arch_vcpu_is_preempted(~owner)) {
>  			smp_yield_cpu(~owner);
>  			first_diag = 0;
>  			continue;
> @@ -81,7 +72,7 @@ void arch_spin_lock_wait(arch_spinlock_t *lp)
>  		 * yield the CPU unconditionally. For LPAR rely on the
>  		 * sense running status.
>  		 */
> -		if (!MACHINE_IS_LPAR || cpu_is_preempted(~owner)) {
> +		if (!MACHINE_IS_LPAR || arch_vcpu_is_preempted(~owner)) {
>  			smp_yield_cpu(~owner);
>  			first_diag = 0;
>  		}
> @@ -108,7 +99,7 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags)
>  			continue;
>  		}
>  		/* Check if the lock owner is running. */
> -		if (first_diag && cpu_is_preempted(~owner)) {
> +		if (first_diag && arch_vcpu_is_preempted(~owner)) {
>  			smp_yield_cpu(~owner);
>  			first_diag = 0;
>  			continue;
> @@ -127,7 +118,7 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags)
>  		 * yield the CPU unconditionally. For LPAR rely on the
>  		 * sense running status.
>  		 */
> -		if (!MACHINE_IS_LPAR || cpu_is_preempted(~owner)) {
> +		if (!MACHINE_IS_LPAR || arch_vcpu_is_preempted(~owner)) {
>  			smp_yield_cpu(~owner);
>  			first_diag = 0;
>  		}
> @@ -165,7 +156,7 @@ void _raw_read_lock_wait(arch_rwlock_t *rw)
>  	owner = 0;
>  	while (1) {
>  		if (count-- <= 0) {
> -			if (owner && cpu_is_preempted(~owner))
> +			if (owner && arch_vcpu_is_preempted(~owner))
>  				smp_yield_cpu(~owner);
>  			count = spin_retry;
>  		}
> @@ -211,7 +202,7 @@ void _raw_write_lock_wait(arch_rwlock_t *rw, unsigned int prev)
>  	owner = 0;
>  	while (1) {
>  		if (count-- <= 0) {
> -			if (owner && cpu_is_preempted(~owner))
> +			if (owner && arch_vcpu_is_preempted(~owner))
>  				smp_yield_cpu(~owner);
>  			count = spin_retry;
>  		}
> @@ -241,7 +232,7 @@ void _raw_write_lock_wait(arch_rwlock_t *rw)
>  	owner = 0;
>  	while (1) {
>  		if (count-- <= 0) {
> -			if (owner && cpu_is_preempted(~owner))
> +			if (owner && arch_vcpu_is_preempted(~owner))
>  				smp_yield_cpu(~owner);
>  			count = spin_retry;
>  		}
> @@ -285,7 +276,7 @@ void arch_lock_relax(unsigned int cpu)
>  {
>  	if (!cpu)
>  		return;
> -	if (MACHINE_IS_LPAR && !cpu_is_preempted(~cpu))
> +	if (MACHINE_IS_LPAR && !arch_vcpu_is_preempted(~cpu))
>  		return;
>  	smp_yield_cpu(~cpu);
>  }
>