On Fri, May 9, 2014 at 1:52 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Friday 09 May 2014 09:32:26 Bjorn Helgaas wrote: >> > 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. > > In most drivers using the streaming DMA API, every mapping is used > exactly once. Think of network or block drivers: they rarely send > the same data twice to the device, and it usually comes from or > goes to some user space buffer. Oh, good point. I don't work that high up in the stack, so thanks for reminding me of that. 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
