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From: Marc Zyngier <maz@kernel.org>
To: Yoan Picchi <yoan.picchi@arm.com>
Cc: catalin.marinas@arm.com, will@kernel.org,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 3/3] KVM: arm64: Add irq_exit counter for kvm_stat
Date: Tue, 20 Apr 2021 14:26:52 +0100	[thread overview]
Message-ID: <878s5dqe77.wl-maz@kernel.org> (raw)
In-Reply-To: <20210420130825.15585-4-yoan.picchi@arm.com>

On Tue, 20 Apr 2021 14:08:25 +0100,
Yoan Picchi <yoan.picchi@arm.com> wrote:
> 
> This counter is meant to detect when the guest vm exits due to an
> interrupt. Those interrupts might be unrelated to the guest VM (say, some
> network packet arrived, and such) but they still trigger an exit which is
> recorded by the "exit" counter. The main purpose of this counter is to
> give some more granularity to this base exit counter so that one can have
> a rough idea of where those exits comes from and so, if those general
> exits happen because of the host or of the guest.

I don't think this makes much sense. Why should we account interrupts
for the guest when the interrupts don't have anything to do with it?
And guess what, they almost *never* do. The only interrupt that could
be accountable to the vcpu is the vPE doorbell, and that one can never
causes an exit, by definition.

The kernel already provides quite a lot around interrupt accounting
already, and I don't think we need to do add more for the guest. If
this made any sense, it should be applicable to any userspace task,
not just vcpus.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Yoan Picchi <yoan.picchi@arm.com>
Cc: james.morse@arm.com, julien.thierry.kdev@gmail.com,
	suzuki.poulose@arm.com, linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, catalin.marinas@arm.com,
	will@kernel.org
Subject: Re: [PATCH v2 3/3] KVM: arm64: Add irq_exit counter for kvm_stat
Date: Tue, 20 Apr 2021 14:26:52 +0100	[thread overview]
Message-ID: <878s5dqe77.wl-maz@kernel.org> (raw)
In-Reply-To: <20210420130825.15585-4-yoan.picchi@arm.com>

On Tue, 20 Apr 2021 14:08:25 +0100,
Yoan Picchi <yoan.picchi@arm.com> wrote:
> 
> This counter is meant to detect when the guest vm exits due to an
> interrupt. Those interrupts might be unrelated to the guest VM (say, some
> network packet arrived, and such) but they still trigger an exit which is
> recorded by the "exit" counter. The main purpose of this counter is to
> give some more granularity to this base exit counter so that one can have
> a rough idea of where those exits comes from and so, if those general
> exits happen because of the host or of the guest.

I don't think this makes much sense. Why should we account interrupts
for the guest when the interrupts don't have anything to do with it?
And guess what, they almost *never* do. The only interrupt that could
be accountable to the vcpu is the vPE doorbell, and that one can never
causes an exit, by definition.

The kernel already provides quite a lot around interrupt accounting
already, and I don't think we need to do add more for the guest. If
this made any sense, it should be applicable to any userspace task,
not just vcpus.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-04-20 13:27 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-20 13:08 [PATCH v2 0/3] KVM: arm64: add more event counters for kvm_stat Yoan Picchi
2021-04-20 13:08 ` Yoan Picchi
2021-04-20 13:08 ` [PATCH v2 1/3] KVM: arm64: Add a stage2 page fault counter " Yoan Picchi
2021-04-20 13:08   ` Yoan Picchi
2021-04-20 13:31   ` Marc Zyngier
2021-04-20 13:31     ` Marc Zyngier
2021-04-20 13:08 ` [PATCH v2 2/3] KVM: arm64: Add two page mapping counters " Yoan Picchi
2021-04-20 13:08   ` Yoan Picchi
2021-04-20 13:52   ` Marc Zyngier
2021-04-20 13:52     ` Marc Zyngier
2021-04-20 13:08 ` [PATCH v2 3/3] KVM: arm64: Add irq_exit counter " Yoan Picchi
2021-04-20 13:08   ` Yoan Picchi
2021-04-20 13:26   ` Marc Zyngier [this message]
2021-04-20 13:26     ` Marc Zyngier

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