linux-kernel - Re: [PATCH] kvm: Enable device LTR/OBFF capibility before doing guest device assignment

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Message-ID: <4FA699F6.9010605@redhat.com>
Date:	Sun, 06 May 2012 18:34:14 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xudong Hao <xudong.hao@...ux.intel.com>
CC:	mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, xiantao.zhang@...el.com,
	xudong.hao@...el.com, Alex Williamson <Alex.Williamson@...hat.com>
Subject: Re: [PATCH] kvm: Enable device LTR/OBFF capibility before doing guest
 device assignment

On 05/06/2012 06:24 PM, Xudong Hao wrote:
> Enable device LTR/OBFF capibility before do device assignment, so that guest can benefit from them.

cc += Alex

> @@ -166,6 +166,10 @@ int kvm_assign_device(struct kvm *kvm,
>     if (pdev == NULL)
>         return -ENODEV;
>
> +   /* Enable some device capibility before do device assignment,
> +    * so that guest can benefit from them.
> +    */
> +   kvm_iommu_enable_dev_caps(pdev);
>     r = iommu_attach_device(domain, &pdev->dev);

Suppose we fail here.  Do we need to disable_dev_caps()?

>     if (r) {
>         printk(KERN_ERR "assign device %x:%x:%x.%x failed",
> @@ -228,6 +232,7 @@ int kvm_deassign_device(struct kvm *kvm,
>         PCI_SLOT(assigned_dev->host_devfn),
>         PCI_FUNC(assigned_dev->host_devfn));
>
> +   kvm_iommu_disable_dev_caps(pdev);
>     return 0;
>  }
>
> @@ -351,3 +356,30 @@ int kvm_iommu_unmap_guest(struct kvm *kvm)
>     iommu_domain_free(domain);
>     return 0;
>  }
> +
> +static void kvm_iommu_enable_dev_caps(struct pci_dev *pdev)
> +{
> +   /* set default value */
> +   unsigned long type = PCI_EXP_OBFF_SIGNAL_ALWAYS;
> +   int snoop_lat_ns = 1024, nosnoop_lat_ns = 1024;

Where does this magic number come from?

> +
> +   /* LTR(Latency tolerance reporting) allows devices to send
> +    * messages to the root complex indicating their latency
> +    * tolerance for snooped & unsnooped memory transactions.
> +    */
> +   pci_enable_ltr(pdev);
> +   pci_set_ltr(pdev, snoop_lat_ns, nosnoop_lat_ns);
> +
> +   /* OBFF (optimized buffer flush/fill), where supported,
> +    * can help improve energy efficiency by giving devices
> +    * information about when interrupts and other activity
> +    * will have a reduced power impact.
> +    */
> +   pci_enable_obff(pdev, type);
> +}
> +
> +static void kvm_iommu_disable_dev_caps(struct pci_dev *pdev)
> +{
> +   pci_disble_obff(pdev);
> +   pci_disble_ltr(pdev);
> +}

Do we need to communicate something about these capabilities to the guest?

-- 
error compiling committee.c: too many arguments to function

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