Re: [Qemu-devel] [PATCH 0/2] vfio: type1 iommu hugepage support

[Alex Williamson <alex.williamson@redhat.com>]

On Sat, 2013-05-25 at 07:21 -0400, Konrad Rzeszutek Wilk wrote:
> On Fri, May 24, 2013 at 11:24:26AM -0600, Alex Williamson wrote:
> > This series let's the vfio type1 iommu backend take advantage of iommu
> > large page support.  See patch 2/2 for the details.  This has been
> > tested on both amd_iommu and intel_iommu, but only my AMD system has
> > large page support.  I'd appreciate any testing and feedback on other
> > systems, particularly vt-d systems supporting large pages.  Mapping
> > efficiency should be improved a bit without iommu hugepages, but I
> > hope that it's much more noticeable with huge pages, especially for
> > very large QEMU guests.
> 
> I took a very very quick look - and I am wondering if there should also
> be a flag to turn it on/off in ther kernel in such case? Especially in the 
> field if a user finds out that their particular IOMMU chipset might
> be doing something funky with large-pages ?

Yeah, that's probably a reasonable feature.  intel-iommu has a boot
option to disable superpages, but we could make it more consistent at
the vfio level if we have a switch there.  It could provided interesting
performance and debugging info.  I'll add a module option to do this.
Thanks,

Alex
 
> > This change includes a clarification to the mapping expectations for
> > users of the type1 iommu, but is compatible with known users and works
> > with existing QEMU userspace supporting vfio.  Thanks,
> > 
> > Alex
> > 
> > ---
> > 
> > Alex Williamson (2):
> >       vfio: Convert type1 iommu to use rbtree
> >       vfio: hugepage support for vfio_iommu_type1
> > 
> > 
> >  drivers/vfio/vfio_iommu_type1.c |  607 ++++++++++++++++++++++++---------------
> >  include/uapi/linux/vfio.h       |    8 -
> >  2 files changed, 387 insertions(+), 228 deletions(-)
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