On Tue, May 20, 2014 at 11:02 AM, Jason Gunthorpe <jgunthorpe@xxxxxxxxxxxxxxxxxxxx> wrote: > On Fri, May 16, 2014 at 08:29:56PM +0000, Karicheri, Muralidharan wrote: > >> But pcie_bus_configure_settings just make sure the mrrs for a device >> is not greater than the max payload size. > > Not quite, it first scans the network checking the Maximum Payload Size > Supported (MPSS) for each device, and chooses the highest supported by > all as the MPS for all. The "performance" setting, e.g., "pci=pcie_bus_perf", adds a few wrinkles by setting MRRS in ways that allow some devices to have larger MPS than others. I don't think this is exactly what was envisioned in the spec, and it is not guaranteed to work if there is peer-to-peer DMA. This isn't documented very well; the best I know of is the changelogs for: a1c473aa11e6 pci: Clamp pcie_set_readrq() when using "performance" settings b03e7495a862 PCI: Set PCI-E Max Payload Size on fabric 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
