> -----Original Message----- > From: Mark Hounschell [mailto:markh@xxxxxxxxxx] > Sent: Friday, May 08, 2015 3:46 PM > To: Konrad Rzeszutek Wilk; William Davis > Cc: linux-pci@xxxxxxxxxxxxxxx; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; jglisse@xxxxxxxxxx; John Hubbard; > Terence Ripperda > Subject: Re: [PATCH 0/6] IOMMU/DMA map_resource support for peer-to-peer > > On 05/08/2015 04:21 PM, Konrad Rzeszutek Wilk wrote: > > On Fri, May 01, 2015 at 01:32:12PM -0500, wdavis@xxxxxxxxxx wrote: > >> From: Will Davis <wdavis@xxxxxxxxxx> > >> > >> Hi, > >> > ... > >> > >> This solves a long-standing problem with the existing DMA-remapping interfaces, > >> which require that a struct page be given for the region to be mapped into a > >> device's IOVA domain. This requirement cannot support peer device BAR ranges, > >> for which no struct pages exist. > >> > ... > >> > >> The Intel and nommu versions have been verified on a dual Intel Xeon E5405 > >> workstation. > > PCIe peer2peer is borked on all motherboards I've tried. Only writes are > possible. Reads are not supported. I suppose if you have a platform with > only PCI and an IOMMU this would be very useful. Without both read and > write PCIe peer2peer support, this seems unnecessary. > PCIe peer-to-peer isn't inherently broken or useless itself, even if a lot of its implementations are; I've successfully tested these patches with existing hardware (dual NVIDIA GPUs + an old-ish workstation), and it solves a longstanding problem for us [1], so I disagree with the assessment that this would be unnecessary. I guess I don't see why the existence of some, or even a lot of, poor implementations suffices as a reason to reject a generic mechanism to support the "good", standardized implementations. [1] http://stackoverflow.com/questions/19841815/does-the-nvidia-rdma-gpudirect-always-operate-only-physical-addresses-in-physic Thanks, Will -- nvpublic -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
