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

[Boqun Feng]

On Fri, Sep 30, 2016 at 12:49:52PM +0800, Pan Xinhui wrote:
> 
> 
> å 2016/9/29 23:51, Christian Borntraeger åé:
> > 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>
> > ---
> 
> 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@ltcalpine2-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

Why do we need a vcpu_is_preempted() implementation for UP? Where will
you use it?

Regards,
Boqun

> ...
> 
> 
> 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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