Hi Dan,
Good to know you've already addressed the struct page issue. We'll watch
out for an updated patchset to try.
On 02/10/15 03:53 PM, Dan Williams wrote:
Hmm, I didn't have peer-to-peer PCI-E in mind for this mechanism, but
the test report is welcome nonetheless. The definition of dma_addr_t
is the device view of host memory, not necessarily the device view of
a peer device's memory range, so I expect you'll run into issues with
IOMMUs and other parts of the kernel that assume this definition.
Yeah, we've actually been doing this with a number of more "hacky"
techniques for some time. ZONE_DEVICE just provides us with a much
cleaner way to set this up that doesn't require patching around
get_user_pages in various places in the kernel.
We've never had any issues with the IOMMU getting in the way (at least
on Intel x86). My understanding always was that the IOMMU sits between a
PCI card and main memory; it doesn't get in the way of peer-to-peer
transfers. Though admittedly, I don't have a complete understanding of
how the IOMMU works in the kernel. I'm just speaking from experimental
experience. We've never actually tried this on other architectures.
Thanks,
Logan
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