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SubjectRe: [PATCH] SR-IOV: correct broken resource alignment calculations
* Matthew Wilcox ( wrote:
> On Fri, Aug 28, 2009 at 12:17:14PM -0700, Chris Wright wrote:
> > An SR-IOV capable device includes an SR-IOV PCIe capability which
> > describes the Virtual Function (VF) BAR requirements. A typical SR-IOV
> > device can support multiple VFs whose BARs must be in a contiguous region,
> > effectively an array of VF BARs. The BAR reports the size requirement
> > for a single VF. We calculate the full range needed by simply multiplying
> > the VF BAR size with the number of possible VFs and create a resource
> > spanning the full range.
> >
> > This all seems sane enough except it artificially inflates the alignment
> > requirement for the VF BAR. The VF BAR need only be aligned to the size
> > of a single BAR not the contiguous range of VF BARs. This can cause us
> > to fail to allocate resources for the BAR despite the fact that we
> > actually have enough space.
> >
> > This patch adds a support for a new resource alignment type,
> > IORESOURCE_VSIZEALIGN, and allows struct resource to keep track of the
> > size requirements of a VF BAR which are smaller than the full resource
> > size. This could also be done all within the PCI layer w/out bloating
> > struct resource or using the last available bit for alignment types.
> Yes, I think that would be preferable. We have a *LOT* of resources in
> the kernel, and the embedded folks would not find it funny if they all
> grew in size suddenly.

OK, I'll send that momentarily. It has one downside which is we re-read
the BAR size multiple times.

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