Re: [PATCH 2/2] kvm: Add ioctl for gathering debug counters

[Alexander Graf <graf@amazon.de>]

On 23.01.20 15:19, Paolo Bonzini wrote:
> On 23/01/20 13:32, Alexander Graf wrote:
>>> See above: I am not sure they are the same story because their consumers
>>> might be very different from registers.  Registers are generally
>>> consumed by programs (to migrate VMs, for example) and only occasionally
>>> by humans, while stats are meant to be consumed by humans.  We may
>>> disagree on whether this justifies a completely different API...
>>
>> I don't fully agree on the "human" part here.
> 
> I agree it's not entirely about humans, but in general it's going to be
> rules and queries on monitoring tools, where 1) the monitoring tools'
> output is generally not KVM-specific, 2) the rules and queries will be
> written by humans.
> 
> So if the kernel produces insn_emulation_fail, the plugin for the
> monitoring tool will just log kvm.insn_emulation_fail.  If the kernel
> produces 0x10042, the plugin will have to convert it and then log it.
> This is why I'm not sure that providing strings is actually less work
> for userspace.

I think we're in agreement then, just leaning onto the other side of the 
same fence. My take is that if I don't know whether a string is 
necessary, I'd rather not have a string :).

I guess as long as we do get stat information out per-vm as well as 
per-vcpu through vmfd and vcpufd, I'm happy overall.

So how strongly do you feel about the string based approach?


Alex

PS: You could btw easily add a "give me the string for a ONE_REG id" 
interface in KVM to translate from 0x10042 to "insn_emulation_fail" :).



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