On Fri, May 09, 2014 at 10:58:50AM +0100, David Woodhouse wrote: > On Thu, 2014-05-08 at 14:30 -0600, Bjorn Helgaas wrote: > > I doubt there would be a noticeable performance effect since these are > > relatively low-frequency interfaces (map, unmap, report_fault), > > That point of view makes me sad. Don't be sad; Arnd successfully fended off the challenge :) > There are people who care deeply about the performance of IOMMU API > map/unmap. It isn't used *just* for virtual machines any more. See > drivers/infiniband/hw/usnic/usnic_uiom.c for example. Of course we should care about IOMMU API performance. We should also care about interface consistency, and it seems there's a tradeoff in this case. I said "relatively" because I expect map/unmap to be less frequent than read/write operations that use the mapping. I don't know anything about infiniband, so maybe that assumption is false there. > I also hold out *some* hope for consolidating the map/unmap functions > for the IOMMU and DMA APIs at some point. The main difference is that > the DMA API allocates an IOVA for itself, while the IOMMU API is given > the bus address too. I find this aspect of these APIs confusing, so I agree that it would be nice if these could be consolidated somehow. Bjorn -- 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
