[vfio-users] Physical vs virtual machine gaming performance comparison benchmarks

[Alex Williamson]

On Sun, Sep 6, 2015 at 5:38 AM, Jon Panozzo <jonp at lime-technology.com>
wrote:

> On Sep 6, 2015 5:54 AM, "Blank Field" <ihatethisfield at gmail.com> wrote:
> > Did you enable HugePages?
>
> No, we don't have hugepages enabled.  We tested hugepages before, but
> honestly didn't see any gains.  We do have transparent pages enabled on the
> host, but our guests do not make use of the <hugepages> XML tag (we use
> libvirt).
>
You really should see a difference from hugepages, it may not be so much in
the graphics performance (this class of system doesn't support hugepages in
the IOMMU), but it allows KVM to skip levels in page table traversals, so
it generally offers a quite apparent performance improvement for any memory
intensive work in the VM.  It may be that 3DMark warms everything
sufficiently that it hides this overhead.  Transparent hugepages are not
effective in a VM with device assignment.  The guest memory is pinned for
the IOMMU, so there's no opportunity later for consolidation.  Thanks,

Alex
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