kvm.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Steven Price <steven.price@arm.com>
To: Christoffer Dall <christoffer.dall@arm.com>
Cc: kvm@vger.kernel.org, linux-doc@vger.kernel.org,
	Marc Zyngier <maz@kernel.org>,
	linux-kernel@vger.kernel.org,
	Russell King <linux@armlinux.org.uk>,
	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 v4 05/10] KVM: arm64: Support stolen time reporting via shared structure
Date: Fri, 30 Aug 2019 10:52:05 +0100	[thread overview]
Message-ID: <bf45fea9-f2f7-1ff3-c90c-cb9623cbd959@arm.com> (raw)
In-Reply-To: <20190830094245.GB5307@e113682-lin.lund.arm.com>

On 30/08/2019 10:42, Christoffer Dall wrote:
> On Fri, Aug 30, 2019 at 09:42:50AM +0100, 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. 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>
[...]
>> +int kvm_update_stolen_time(struct kvm_vcpu *vcpu, bool init)
>> +{
>> +	struct kvm *kvm = vcpu->kvm;
>> +	u64 steal;
>> +	u64 steal_le;
>> +	u64 offset;
>> +	int idx;
>> +	u64 base = vcpu->arch.steal.base;
>> +
>> +	if (base == GPA_INVALID)
>> +		return -ENOTSUPP;
>> +
>> +	/* Let's do the local bookkeeping */
>> +	steal = vcpu->arch.steal.steal;
>> +	steal += current->sched_info.run_delay - vcpu->arch.steal.last_steal;
>> +	vcpu->arch.steal.last_steal = current->sched_info.run_delay;
>> +	vcpu->arch.steal.steal = steal;
>> +
>> +	steal_le = cpu_to_le64(steal);
>> +	idx = srcu_read_lock(&kvm->srcu);
>> +	if (init) {
>> +		struct pvclock_vcpu_stolen_time init_values = {
>> +			.revision = 0,
>> +			.attributes = 0
>> +		};
>> +		kvm_write_guest(kvm, base, &init_values,
>> +				sizeof(init_values));
>> +	}
>> +	offset = offsetof(struct pvclock_vcpu_stolen_time, stolen_time);
>> +	kvm_put_guest(kvm, base + offset, steal_le, u64);
> 
> Let's hope we don't have thousands of memslots through which we have to
> do a linear scan on every vcpu load after this.  If that were the case,
> I think the memslot search path would have to be updated anyhow.

Yes I'm not sure with the current memslot implementation it is actually
beneficial to split up the stolen time structures into separate
memslots. But there's nothing requiring the use of so many memslots.

If this is really a problem it would be possible to implement a
memslot-caching kvm_put_guest(), but I'd want to wait until someone
shows there's actually a problem first.

> Otherwise looks reasonable to me.

Great, thanks for the review.

Steve

  reply	other threads:[~2019-08-30  9:52 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-30  8:42 [PATCH v4 00/10] arm64: Stolen time support Steven Price
2019-08-30  8:42 ` [PATCH v4 01/10] KVM: arm64: Document PV-time interface Steven Price
2019-08-30 14:47   ` Andrew Jones
2019-08-30 15:25     ` Steven Price
2019-09-02 12:52       ` Andrew Jones
2019-09-04 13:55         ` Steven Price
2019-09-04 14:22           ` Andrew Jones
2019-09-04 15:07             ` Steven Price
2019-08-30  8:42 ` [PATCH v4 02/10] KVM: arm/arm64: Factor out hypercall handling from PSCI code Steven Price
2019-09-02  7:06   ` kbuild test robot
2019-09-04 15:05     ` Steven Price
2019-09-02 13:07   ` kbuild test robot
2019-08-30  8:42 ` [PATCH v4 03/10] KVM: arm64: Implement PV_FEATURES call Steven Price
2019-08-30  8:42 ` [PATCH v4 04/10] KVM: Implement kvm_put_guest() Steven Price
2019-08-30  8:42 ` [PATCH v4 05/10] KVM: arm64: Support stolen time reporting via shared structure Steven Price
2019-08-30  9:42   ` Christoffer Dall
2019-08-30  9:52     ` Steven Price [this message]
2019-09-03  9:14   ` Zenghui Yu
2019-09-04 15:53     ` Steven Price
2019-08-30  8:42 ` [PATCH v4 06/10] KVM: Allow kvm_device_ops to be const Steven Price
2019-08-30  8:42 ` [PATCH v4 07/10] KVM: arm64: Provide VCPU attributes for stolen time Steven Price
2019-08-30 10:02   ` Marc Zyngier
2019-08-30 15:04     ` Steven Price
2019-08-30  8:42 ` [PATCH v4 08/10] arm/arm64: Provide a wrapper for SMCCC 1.1 calls Steven Price
2019-08-30  8:42 ` [PATCH v4 09/10] arm/arm64: Make use of the SMCCC 1.1 wrapper Steven Price
2019-08-30  8:42 ` [PATCH v4 10/10] arm64: Retrieve stolen time as paravirtualized guest Steven Price
2019-09-03  8:47   ` Andrew Jones
2019-09-04 16:01     ` Steven Price
2019-09-03  8:03 ` [PATCH v4 00/10] arm64: Stolen time support Andrew Jones
2019-09-03  8:49   ` Andrew Jones
2019-09-04 16:02     ` Steven Price

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=bf45fea9-f2f7-1ff3-c90c-cb9623cbd959@arm.com \
    --to=steven.price@arm.com \
    --cc=catalin.marinas@arm.com \
    --cc=christoffer.dall@arm.com \
    --cc=kvm@vger.kernel.org \
    --cc=kvmarm@lists.cs.columbia.edu \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux@armlinux.org.uk \
    --cc=maz@kernel.org \
    --cc=pbonzini@redhat.com \
    --cc=will@kernel.org \
    --subject='Re: [PATCH v4 05/10] KVM: arm64: Support stolen time reporting via shared structure' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).