Re: [PATCH 1/1] KVM: s390: provide counters for all interrupt injects/delivery

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On 03/09/2018 10:18 AM, Cornelia Huck wrote:
> On Thu,  8 Mar 2018 13:30:09 +0000
> Christian Borntraeger <borntraeger@xxxxxxxxxx> wrote:
> 
>> For testing the exitless interrupt support it turned out useful to
>> have separate counters for inject and delivery of I/O interrupt.
>> While at it do the same for all interrupt types. For timer
>> related interrupts (clock comparator and cpu timer) we even had
>> no delivery counters. Fix this as well. On this way some counters
>> are being renamed to have a similar name.
> 
> Seems reasonable if you rely on the counters to have them cover
> everything. Some meta-questions, though:
> 
> - A lot of the places are also covered by trace events and/or dbf
>   events. These can add more information (like payload etc.), but are
>   not as lightweight as the counters. Does it also make sense to fill
>   in any gaps in that infrastructure? Or aren't they used as much? (I
>   haven't done much kvm debugging recently, so I'm probably not the
>   person to judge their usefulness.)

In the end you will have a customer or QA issue that will require exactly
that missing event to understand whats going on (Thats why I add these
counters now).
So yes, we might want to add more traces and/or dbf statements. This needs
more work though, as both are more costly (e.g. dbf takes a spinlock) and/or
need explicit enablement or the correct level. I will have a look.
> 
> (more below...)
> 
>>
>> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
>> ---
>>  arch/s390/include/asm/kvm_host.h | 25 +++++++++++++++++++++----
>>  arch/s390/kvm/interrupt.c        | 25 +++++++++++++++++++++----
>>  arch/s390/kvm/kvm-s390.c         | 24 +++++++++++++++++++++---
>>  3 files changed, 63 insertions(+), 11 deletions(-)
> 
> (...)
> 
>> @@ -1328,6 +1332,7 @@ static int __inject_extcall(struct kvm_vcpu *vcpu, struct kvm_s390_irq *irq)
>>  	struct kvm_s390_extcall_info *extcall = &li->irq.extcall;
>>  	uint16_t src_id = irq->u.extcall.code;
>>  
>> +	vcpu->stat.inject_external_call++;
>>  	VCPU_EVENT(vcpu, 4, "inject: external call source-cpu:%u",
>>  		   src_id);
>>  	trace_kvm_s390_inject_vcpu(vcpu->vcpu_id, KVM_S390_INT_EXTERNAL_CALL,
> 
> Some of the injection functions (like this one) can return an error.
> There does not seem to be any tracing of those failures, though. Would
> it be helpful for at least some cases, or is that overkill?

Hmm, that could be interesting, but it requires additional review to 
identify the proper places. I will see if I can come up with a followup
patch later.

> 
> Patch looks good to me, so
> 
> Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>
> 

Thanks.

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