Re: pci-sysfs resource mmap broken (and PATCH)

From: Benjamin Herrenschmidt
Date: Thu Apr 28 2005 - 02:52:52 EST

On Thu, 2005-04-28 at 00:22 -0700, David S. Miller wrote:
> On Thu, 28 Apr 2005 17:21:19 +1000
> Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> wrote:
> > I have a real net big performance improvement on X by doing that
> > trick ... the sysfs mmap API doesn't really provide a mean to do
> > it explicitely from userland (unlike the ioctl with the old proc api)
> You can refine your test to "if PCI class is display or VGA" and the
> prefetchability is set in the BAR, then elide the guard PTE
> protection bit.

Yes, but I was also thinking about some of those Myrinet kind of things
who also provide large PCI shared memory region ...

I may end up adding an explicit list of classes/vid/did that are
"allowed" to use the trick to avoid problems.


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