Re: [PATCH] KVM: s390: change default halt poll to 50000

[Janosch Frank <frankja@linux.ibm.com>]

On 5/15/19 12:22 PM, David Hildenbrand wrote:
> "KVM: s390: change default halt poll time to 50us
> 
> Recent measurements indicate that using 50us results in a reduced CPU
> consumption, while still providing the benefit of halt polling. Let's
> use 50us instead."
> 
> Acked-by: David Hildenbrand <david@redhat.com>

With that change:
Acked-by: Janosch Frank <frankja@linux.vnet.ibm.com>

> 
> 
> 
> On 15.05.19 10:23, Christian Borntraeger wrote:
>> older performance measurements indicated that 50000 vs 80000 reduces cpu
>> consumption while still providing the benefit of halt polling. We had
>> this change in the IBM KVM product, but it got lost so it never went
>> upstream. Recent re-measurement indicate that 50k is still better than
>> 80k.>
>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> ---
>>  arch/s390/include/asm/kvm_host.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>> index dbe254847e0d..cb63cc7bbf06 100644
>> --- a/arch/s390/include/asm/kvm_host.h
>> +++ b/arch/s390/include/asm/kvm_host.h
>> @@ -36,7 +36,7 @@
>>   */
>>  #define KVM_NR_IRQCHIPS 1
>>  #define KVM_IRQCHIP_NUM_PINS 4096
>> -#define KVM_HALT_POLL_NS_DEFAULT 80000
>> +#define KVM_HALT_POLL_NS_DEFAULT 50000
>>  
>>  /* s390-specific vcpu->requests bit members */
>>  #define KVM_REQ_ENABLE_IBS	KVM_ARCH_REQ(0)
>>
> 
>