Re: [PATCH] powerpc/sched: Cleanup vcpu_is_preempted()

[Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>]

On 11/14/23 2:53 PM, Shrikanth Hegde wrote:
> 
> 
> On 11/14/23 12:42 PM, Aneesh Kumar K.V wrote:
>> No functional change in this patch. A helper is added to find if
>> vcpu is dispatched by hypervisor. Use that instead of opencoding.
>> Also clarify some of the comments.
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> ---
>>  arch/powerpc/include/asm/paravirt.h | 33 ++++++++++++++++++++++-------
>>  1 file changed, 25 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/paravirt.h b/arch/powerpc/include/asm/paravirt.h
>> index ac4279208d63..b78b82d66057 100644
>> --- a/arch/powerpc/include/asm/paravirt.h
>> +++ b/arch/powerpc/include/asm/paravirt.h
>> @@ -76,6 +76,17 @@ static inline bool is_vcpu_idle(int vcpu)
>>  {
>>  	return lppaca_of(vcpu).idle;
>>  }
>> +
>> +static inline bool vcpu_is_dispatched(int vcpu)
>> +{
>> +	/*
>> +	 * This is the yield_count.  An "odd" value (low bit on) means that
>> +	 * the processor is yielded (either because of an OS yield or a
>> +	 * hypervisor preempt).  An even value implies that the processor is
>> +	 * currently executing.
>> +	 */
>> +	return (!(yield_count_of(vcpu) & 1));
>> +}
>>  #else
>>  static inline bool is_shared_processor(void)
>>  {
>> @@ -109,6 +120,10 @@ static inline bool is_vcpu_idle(int vcpu)
>>  {
>>  	return false;
>>  }
>> +static inline bool vcpu_is_dispatched(int vcpu)
>> +{
>> +	return true;
>> +}
>>  #endif
>>
> 
> Similar code can be changed in lib/qspinlock.c and lib/locks.c as well. 

I avoided doing that because they used the fetched yield_count value

yield_to_preempted(owner, yield_count);


and the checking comes with a comment

	if ((yield_count & 1) == 0)
		goto relax; /* owner vcpu is running */


-aneesh