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From: Krish Sadhukhan <krish.sadhukhan@oracle.com>
To: Jim Mattson <jmattson@google.com>
Cc: kvm list <kvm@vger.kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>
Subject: Re: [PATCH 2/3] KVM: nVMX: Add a new VCPU statistic to show if VCPU is running nested guest
Date: Wed, 12 May 2021 10:56:14 -0700	[thread overview]
Message-ID: <c5c4a9d2-73b5-69eb-58ee-c52df4c2ff18@oracle.com> (raw)
In-Reply-To: <CALMp9eTCgEG=kkQTn+g=DqniLq+RRmzp7jeK_iexoq++qiraxQ@mail.gmail.com>


On 5/12/21 9:01 AM, Jim Mattson wrote:
> On Tue, May 11, 2021 at 7:37 PM Krish Sadhukhan
> <krish.sadhukhan@oracle.com> wrote:
>> Add the following per-VCPU statistic to KVM debugfs to show if a given
>> VCPU is running a nested guest:
>>
>>          nested_guest_running
>>
>> Also add this as a per-VM statistic to KVM debugfs to show the total number
>> of VCPUs running a nested guest in a given VM.
>>
>> Signed-off-by: Krish Sadhukhan <Krish.Sadhukhan@oracle.com>
> This is fine, but I don't really see its usefulness. OTOH, one

Two potential uses:

     1. If Live Migration of L2 guests is broken/buggy, this can be used 
to determine a safer time to trigger Live Migration of L1 guests.

     2. This can be used to create a time-graph of the load of L1 and L2 
in a given VM as well across the host.

> statistic I would really like to see is how many vCPUs have *ever* run
> a nested guest.

'nested_runs' statistic provides this data, though only till VCPUs are 
alive. We can convert 'nested_runs' to be persistent beyond VCPU 
destruction.

But I am curious about the usage you are thinking of with this.


  reply	other threads:[~2021-05-12 19:44 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-12  1:47 [PATCH 0/3] KVM: nVMX: Add more statistics to KVM debugfs Krish Sadhukhan
2021-05-12  1:47 ` [PATCH 1/3] KVM: nVMX: Move 'nested_run' counter to enter_guest_mode() Krish Sadhukhan
2021-05-12 18:30   ` Sean Christopherson
2021-05-13 16:02     ` Dongli Zhang
2021-05-12  1:47 ` [PATCH 2/3] KVM: nVMX: Add a new VCPU statistic to show if VCPU is running nested guest Krish Sadhukhan
2021-05-12 16:01   ` Jim Mattson
2021-05-12 17:56     ` Krish Sadhukhan [this message]
2021-05-12 17:59       ` Jim Mattson
2021-05-12 18:19       ` Sean Christopherson
2021-05-12  1:47 ` [PATCH 3/3] KVM: x86: Add a new VM statistic to show number of VCPUs created in a given VM Krish Sadhukhan

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