We have developed a proof of concept for allowing a PCI Express device attached to one computer to be used by another computer without any software intermediate on the data path. The device driver runs on a physically separate machine from the device, but our implementation allows the device driver and device to communicate as if the device and driver were in the same machine, without modifying either the driver or the device. The kernel and higher level software can utilize the device as if it were a local device. A device will not be used by two separate machines at the same time, but a machine can transfer the control of a local device to a remote machine. We have named this concept "device lending". We envision that machines will have, in addition to local PCIe devices, access to a pool of remote PCIe devices. When a machine needs more device resources, additional devices can be dynamically borrowed from other machines with devices to spare. These devices can be located in a dedicated external cabinet, or be devices inserted into internal slots in a normal computer. The device lending is implemented using a Non-Transparent Bridge (NTB), a native PCIe interconnect that should offer performance close to that of a locally connected device. Devices that are not currently being lent to another host will not be affected in any way. NTBs are available as add-ons for any PCIe based computer and are included in newer Intel Xeon CPUs. The proof of concept we created was implemented for Linux, on top of the APIs provided by our NTB vendor, Dolphin. The host borrowing a device has a kernel module to provide the necessary software support and the other host has a user space daemon. No additional software modifications or hardware is required, nor special support from the devices. The current implementation works with some devices, but has some problems with others. We believe however, that we have identified the problems and how to improve the situation. In a later implementation, we believe that all devices we have tested can be made to work correctly and with very high performance
