KVM: s390: change default halt poll to 50000
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Message ID 20190515082324.112755-1-borntraeger@de.ibm.com
State New
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  • KVM: s390: change default halt poll to 50000
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Commit Message

Christian Borntraeger May 15, 2019, 8:23 a.m. UTC
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(-)

Comments

David Hildenbrand May 15, 2019, 10:22 a.m. UTC | #1
"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>



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)
>
Christian Borntraeger May 15, 2019, 10:26 a.m. UTC | #2
On 15.05.19 12:22, 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."

Yes, sounds better.
> 
> Acked-by: David Hildenbrand <david@redhat.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)
>>
> 
>
Janosch Frank May 15, 2019, 10:55 a.m. UTC | #3
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)
>>
> 
>
Cornelia Huck May 15, 2019, 11:34 a.m. UTC | #4
On Wed, 15 May 2019 10:23:24 +0200
Christian Borntraeger <borntraeger@de.ibm.com> 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)

I trust your tests :)

Acked-by: Cornelia Huck <cohuck@redhat.com>

Patch
diff mbox series

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)