From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: Having troubles binding an SR-IOV VF to
 uio_pci_generic on Amazon instance
Date: Fri, 2 Oct 2015 16:50:15 +0300
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Cc: "dev@dpdk.org" <dev@dpdk.org>, Avi Kivity <avi@scylladb.com>
To: Alexander Duyck <alexander.duyck@gmail.com>
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On Thu, Oct 01, 2015 at 02:17:49PM -0700, Alexander Duyck wrote:
> On 10/01/2015 02:42 AM, Michael S. Tsirkin wrote:
> >On Thu, Oct 01, 2015 at 12:22:46PM +0300, Avi Kivity wrote:
> >>even when they are some users
> >>prefer to avoid the performance penalty.
> >I don't think there's a measureable penalty from passing through the
> >IOMMU, as long as mappings are mostly static (i.e. iommu=pt).  I sure
> >never saw any numbers that show such.
> 
> It depends on the IOMMU.  I believe Intel had a performance penalty on all
> CPUs prior to Ivy Bridge.  Since then things have improved to where they are
> comparable to bare metal.
> 
> The graph on page 5 of
> https://networkbuilders.intel.com/docs/Network_Builders_RA_vBRAS_Final.pdf
> shows the penalty clear as day.  Pretty much anything before Ivy Bridge w/
> small packets is slowed to a crawl with an IOMMU enabled.
> 
> - Alex

VMs are running with IOMMU enabled anyway.
Avi here tells us no one uses SRIOV on bare metal so ...
we don't need to argue about that.

-- 
MST