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From: Steven Price <steven.price@arm.com>
To: Jonathan Cameron <jonathan.cameron@huawei.com>
Cc: "Mark Rutland" <mark.rutland@arm.com>,
	kvm@vger.kernel.org, "Radim Krčmář" <rkrcmar@redhat.com>,
	"Marc Zyngier" <maz@kernel.org>,
	"Suzuki K Pouloze" <suzuki.poulose@arm.com>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Russell King" <linux@armlinux.org.uk>,
	"James Morse" <james.morse@arm.com>,
	"Julien Thierry" <julien.thierry.kdev@gmail.com>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Will Deacon" <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 05/10] KVM: arm64: Support stolen time reporting via shared structure
Date: Thu, 22 Aug 2019 12:00:54 +0100	[thread overview]
Message-ID: <301610cc-ba04-89d6-a0b6-d37ecf4a717a@arm.com> (raw)
In-Reply-To: <20190822113942.0000701f@huawei.com>

On 22/08/2019 11:39, Jonathan Cameron wrote:
> On Wed, 21 Aug 2019 16:36:51 +0100
> Steven Price <steven.price@arm.com> 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. 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@arm.com>
> 
> One totally trivial comment inline... Feel free to ignore :)
> 
[...]
>> +int kvm_hypercall_stolen_time(struct kvm_vcpu *vcpu)
>> +{
>> +	u64 ret;
>> +	int err;
>> +
>> +	/*
>> +	 * Start counting stolen time from the time the guest requests
>> +	 * the feature enabled.
>> +	 */
>> +	vcpu->arch.steal.steal = 0;
>> +	vcpu->arch.steal.last_steal = current->sched_info.run_delay;
>> +
>> +	err = kvm_update_stolen_time(vcpu, true);
>> +
>> +	if (err)
>> +		ret = SMCCC_RET_NOT_SUPPORTED;
> 
> Trivial by why not
> 		return SMCCC_RET_NOT_SUPPORTED;
> 
> 	return vcpu->kvm->arch.pvtime.st_base +
> ...
> Drops the indentation a bit and puts the error handling out of
> line which is slightly nicer to read (to my eyes).

Yes that's a nice change - drops the extra "ret" variable too.

Thanks,

Steve

  reply	other threads:[~2019-08-22 11:01 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-21 15:36 [PATCH v3 00/10] arm64: Stolen time support Steven Price
2019-08-21 15:36 ` [PATCH v3 01/10] KVM: arm64: Document PV-time interface Steven Price
2019-08-27  8:44   ` Christoffer Dall
2019-08-28 11:23     ` Steven Price
2019-08-27  8:57   ` Christoffer Dall
2019-08-28 12:09     ` Steven Price
2019-08-30  9:22       ` Christoffer Dall
2019-08-28 13:49     ` Christoffer Dall
2019-08-29 15:21       ` Steven Price
2019-08-29 17:15   ` Andrew Jones
2019-08-30  8:35     ` Steven Price
2019-08-21 15:36 ` [PATCH v3 02/10] KVM: arm/arm64: Factor out hypercall handling from PSCI code Steven Price
2019-08-21 15:36 ` [PATCH v3 03/10] KVM: arm64: Implement PV_FEATURES call Steven Price
2019-08-21 15:36 ` [PATCH v3 04/10] KVM: Implement kvm_put_guest() Steven Price
2019-08-22 10:29   ` Jonathan Cameron
2019-08-22 10:37     ` Steven Price
2019-08-22 15:28   ` Sean Christopherson
2019-08-22 15:46     ` Steven Price
2019-08-22 16:24       ` Sean Christopherson
2019-08-23 10:33         ` Steven Price
2019-08-21 15:36 ` [PATCH v3 05/10] KVM: arm64: Support stolen time reporting via shared structure Steven Price
2019-08-22 10:39   ` Jonathan Cameron
2019-08-22 11:00     ` Steven Price [this message]
2019-08-23 12:07   ` Zenghui Yu
2019-08-23 13:23     ` Steven Price
2019-08-21 15:36 ` [PATCH v3 06/10] KVM: Allow kvm_device_ops to be const Steven Price
2019-08-21 15:36 ` [PATCH v3 07/10] KVM: arm64: Provide a PV_TIME device to user space Steven Price
2019-08-22 10:57   ` Jonathan Cameron
2019-08-22 11:11     ` Steven Price
2019-08-22 11:48       ` Jonathan Cameron
2019-08-21 15:36 ` [PATCH v3 08/10] arm/arm64: Provide a wrapper for SMCCC 1.1 calls Steven Price
2019-08-21 15:36 ` [PATCH v3 09/10] arm/arm64: Make use of the SMCCC 1.1 wrapper Steven Price
2019-08-21 15:36 ` [PATCH v3 10/10] arm64: Retrieve stolen time as paravirtualized guest Steven Price
2019-08-23 11:45   ` Zenghui Yu
2019-08-23 14:22     ` Steven Price
2019-08-27 12:43       ` Zenghui Yu

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