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.
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prev parent reply other threads:[~2021-04-20 13:29 UTC|newest]
Thread overview: 7+ 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 ` [PATCH v2 1/3] KVM: arm64: Add a stage2 page fault counter " Yoan Picchi
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 13:52 ` Marc Zyngier
2021-04-20 13:08 ` [PATCH v2 3/3] KVM: arm64: Add irq_exit counter " Yoan Picchi
2021-04-20 13:26 ` Marc Zyngier [this message]
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