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Date:   Fri, 30 Sep 2016 12:49:52 +0800
From:   Pan Xinhui <xinhui@...ux.vnet.ibm.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>
Cc:     Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        xen-devel-request@...ts.xenproject.org, benh@...nel.crashing.org,
        paulus@...ba.org, mpe@...erman.id.au, mingo@...hat.com,
        paulmck@...ux.vnet.ibm.com, will.deacon@....com,
        kernellwp@...il.com, jgross@...e.com, pbonzini@...hat.com,
        bsingharora@...il.com
Subject: Re: [PATCH v2 1/1] s390/spinlock: Provide vcpu_is_preempted



在 2016/9/29 23:51, Christian Borntraeger 写道:
> 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@...ibm.com>
> ---

hi, Christian
	thanks for your patch!

>  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)
  
root@...alpine2-lp13:~/linux# git grep -wn smp_vcpu_scheduled arch/s390/
arch/s390/include/asm/smp.h:34:extern int smp_vcpu_scheduled(int cpu);
arch/s390/include/asm/smp.h:56:static inline int smp_vcpu_scheduled(int cpu) { return 1; }
arch/s390/kernel/smp.c:371:int smp_vcpu_scheduled(int cpu)
arch/s390/lib/spinlock.c:44:    if (smp_vcpu_scheduled(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;
I saw smp_vcpu_scheduled() returns true always on !SMP system.

maybe we can do somegthing silimar. like below

#ifndef CONFIG_SMP
static inline bool arch_vcpu_is_preempted(int cpu) { return !test_cpu_flag_of(CIF_ENABLED_WAIT, cpu); }
#else
...

but I can't help thinking that if this is a!SMP system, maybe we could only
#ifndef CONFIG_SMP
static inline bool arch_vcpu_is_preempted(int cpu) { return false; }
#else
...


thanks
xinhui

> +	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);
>  }
>

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