linux-kernel - Re: [PATCH v4 05/10] KVM: arm64: Support stolen time reporting via shared structure

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Date:   Wed, 4 Sep 2019 16:53:02 +0100
From:   Steven Price <steven.price@....com>
To:     Zenghui Yu <yuzenghui@...wei.com>, Marc Zyngier <maz@...nel.org>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        linux-doc@...r.kernel.org, Russell King <linux@...linux.org.uk>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v4 05/10] KVM: arm64: Support stolen time reporting via
 shared structure

On 03/09/2019 10:14, Zenghui Yu wrote:
> On 2019/8/30 16:42, Steven Price wrote:
>> Implement the service call for configuring a shared structure between a
>> VCPU and the hypervisor in which the hypervisor can write the time
>> stolen from the VCPU's execution time by other tasks on the host.
>>
>> The hypervisor allocates memory which is placed at an IPA chosen by user
>> space.
> 
> It seems that no allocation happens in the hypervisor code.  User space
> will do it instead?

Ah, yes I should update the commit message. User space does now allocate
the memory. Thanks for spotting that.

Steve

>> The hypervisor then updates the shared structure using
>> kvm_put_guest() to ensure single copy atomicity of the 64-bit value
>> reporting the stolen time in nanoseconds.
>>
>> Whenever stolen time is enabled by the guest, the stolen time counter is
>> reset.
>>
>> The stolen time itself is retrieved from the sched_info structure
>> maintained by the Linux scheduler code. We enable SCHEDSTATS when
>> selecting KVM Kconfig to ensure this value is meaningful.
>>
>> Signed-off-by: Steven Price <steven.price@....com>
> 
> Thanks,
> zenghui
>