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

[Pan Xinhui <xinhui@linux.vnet.ibm.com>]

在 2016/9/30 13:52, Boqun Feng 写道:
> On Fri, Sep 30, 2016 at 12:49:52PM +0800, Pan Xinhui wrote:
>>
>>
>> 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@de.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@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?
>
yep, I also wonder that :)

But there is a definitaion of smp_vcpu_scheduled() for !SMP kernel.
So I am a little worried that some code has included this spinlock.h for UP kernel also.

Hi, Christian
	Could you help confirms that your patch works on UP? :)

thanks
xinhui

> 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);
>>>  }
>>>
>>