Re: [PATCH] KVM: s390: filter and count invalid yields

[David Hildenbrand <david@redhat.com>]

On 10.10.19 12:21, Christian Borntraeger wrote:
> To analyze some performance issues with lock contention and scheduling
> it is nice to know when diag9c did not result in any action.
> At the same time avoid calling the scheduler (which can be expensive)
> if we know that it does not make sense.
> 
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> ---
>  arch/s390/include/asm/kvm_host.h |  2 ++
>  arch/s390/kvm/diag.c             | 23 +++++++++++++++++++----
>  arch/s390/kvm/kvm-s390.c         |  2 ++
>  3 files changed, 23 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index abe60268335d..743cd5a63b37 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -392,6 +392,8 @@ struct kvm_vcpu_stat {
>  	u64 diagnose_10;
>  	u64 diagnose_44;
>  	u64 diagnose_9c;
> +	u64 diagnose_9c_success;
> +	u64 diagnose_9c_ignored;

Can't you derive the one from the other with diagnose_9c? Just sayin,
one would be sufficient.

>  	u64 diagnose_258;
>  	u64 diagnose_308;
>  	u64 diagnose_500;
> diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
> index 45634b3d2e0a..2c729f020585 100644
> --- a/arch/s390/kvm/diag.c
> +++ b/arch/s390/kvm/diag.c
> @@ -158,14 +158,29 @@ static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu)
>  
>  	tid = vcpu->run->s.regs.gprs[(vcpu->arch.sie_block->ipa & 0xf0) >> 4];
>  	vcpu->stat.diagnose_9c++;
> -	VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d", tid);
>  
> +	/* yield to self */
>  	if (tid == vcpu->vcpu_id)
> -		return 0;
> +		goto no_yield;
>  
> +	/* yield to invalid */
>  	tcpu = kvm_get_vcpu_by_id(vcpu->kvm, tid);
> -	if (tcpu)
> -		kvm_vcpu_yield_to(tcpu);
> +	if (!tcpu)
> +		goto no_yield;
> +
> +	/* target already running */
> +	if (tcpu->cpu >= 0)
> +		goto no_yield;

Wonder if it's wort moving this optimization to a separate patch.

> +
> +	if (kvm_vcpu_yield_to(tcpu) <= 0)
> +		goto no_yield;
> +
> +	VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d: done", tid);
> +	vcpu->stat.diagnose_9c_success++;
> +	return 0;
> +no_yield:
> +	VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d: ignored", tid);
> +	vcpu->stat.diagnose_9c_ignored++;
>  	return 0;
>  }
>  
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 4a3bc40ca1a4..b368e835f2f7 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -155,6 +155,8 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
>  	{ "instruction_diag_10", VCPU_STAT(diagnose_10) },
>  	{ "instruction_diag_44", VCPU_STAT(diagnose_44) },
>  	{ "instruction_diag_9c", VCPU_STAT(diagnose_9c) },
> +	{ "diag_9c_success", VCPU_STAT(diagnose_9c_success) },
> +	{ "diag_9c_ignored", VCPU_STAT(diagnose_9c_ignored) },
>  	{ "instruction_diag_258", VCPU_STAT(diagnose_258) },
>  	{ "instruction_diag_308", VCPU_STAT(diagnose_308) },
>  	{ "instruction_diag_500", VCPU_STAT(diagnose_500) },
> 


-- 

Thanks,

David / dhildenb