Hello, This is a continuation of our work to enable using Peer-to-Peer PCI memory in NVMe fabrics targets. Many thanks go to Christoph Hellwig who provided valuable feedback to get these patches to where they are today.
The concept here is to use memory that's exposed on a PCI BAR as data buffers in the NVME target code such that data can be transferred from an RDMA NIC to the special memory and then directly to an NVMe device avoiding system memory entirely. The upside of this is better QoS for applications running on the CPU utilizing memory and lower PCI bandwidth required to the CPU (such that systems could be designed with fewer lanes connected to the CPU). However, presently, the trade-off is currently a reduction in overall throughput. (Largely due to hardware issues that would certainly improve in the future). Due to these trade-offs we've designed the system to only enable using the PCI memory in cases where the NIC, NVMe devices and memory are all behind the same PCI switch. This will mean many setups that could likely work well will not be supported so that we can be more confident it will work and not place any responsibility on the user to understand their topology. (We chose to go this route based on feedback we received at the last LSF). Future work may enable these transfers behind a fabric of PCI switches or perhaps using a white list of known good root complexes. In order to enable this functionality, we introduce a few new PCI functions such that a driver can register P2P memory with the system. Struct pages are created for this memory using devm_memremap_pages() and the PCI bus offset is stored in the corresponding pagemap structure. Another set of functions allow a client driver to create a list of client devices that will be used in a given P2P transactions and then use that list to find any P2P memory that is supported by all the client devices. This list is then also used to selectively disable the ACS bits for the downstream ports behind these devices. In the block layer, we also introduce a P2P request flag to indicate a given request targets P2P memory as well as a flag for a request queue to indicate a given queue supports targeting P2P memory. P2P requests will only be accepted by queues that support it. Also, P2P requests are marked to not be merged seeing a non-homogenous request would complicate the DMA mapping requirements. In the PCI NVMe driver, we modify the existing CMB support to utilize the new PCI P2P memory infrastructure and also add support for P2P memory in its request queue. When a P2P request is received it uses the pci_p2pmem_map_sg() function which applies the necessary transformation to get the corrent pci_bus_addr_t for the DMA transactions. In the RDMA core, we also adjust rdma_rw_ctx_init() and rdma_rw_ctx_destroy() to take a flags argument which indicates whether to use the PCI P2P mapping functions or not. Finally, in the NVMe fabrics target port we introduce a new configuration boolean: 'allow_p2pmem'. When set, the port will attempt to find P2P memory supported by the RDMA NIC and all namespaces. If supported memory is found, it will be used in all IO transfers. And if a port is using P2P memory, adding new namespaces that are not supported by that memory will fail. This series is based off of Christoph's v3 series to revamp dev_pagemap. A git repo of the patches is available here[2]. Logan Christoph Hellwig (2): nvme-pci: clean up CMB initialization nvme-pci: clean up SMBSZ bit definitions Logan Gunthorpe (10): pci-p2p: Support peer to peer memory pci-p2p: Add sysfs group to display p2pmem stats pci-p2p: Add PCI p2pmem dma mappings to adjust the bus offset pci-p2p: Clear ACS P2P flags for all client devices block: Introduce PCI P2P flags for request and request queue IB/core: Add optional PCI P2P flag to rdma_rw_ctx_[init|destroy]() nvme-pci: Use PCI p2pmem subsystem to manage the CMB nvme-pci: Add support for P2P memory in requests nvme-pci: Add a quirk for a pseudo CMB nvmet: Optionally use PCI P2P memory Documentation/ABI/testing/sysfs-bus-pci | 25 + block/blk-core.c | 3 + drivers/infiniband/core/rw.c | 22 +- drivers/infiniband/ulp/isert/ib_isert.c | 5 +- drivers/infiniband/ulp/srpt/ib_srpt.c | 7 +- drivers/nvme/host/core.c | 4 + drivers/nvme/host/nvme.h | 8 + drivers/nvme/host/pci.c | 164 ++++--- drivers/nvme/target/configfs.c | 29 ++ drivers/nvme/target/core.c | 95 +++- drivers/nvme/target/io-cmd.c | 3 + drivers/nvme/target/nvmet.h | 10 + drivers/nvme/target/rdma.c | 41 +- drivers/pci/Kconfig | 14 + drivers/pci/Makefile | 1 + drivers/pci/p2p.c | 781 ++++++++++++++++++++++++++++++++ include/linux/blk_types.h | 18 +- include/linux/blkdev.h | 2 + include/linux/memremap.h | 19 + include/linux/nvme.h | 22 +- include/linux/pci-p2p.h | 94 ++++ include/linux/pci.h | 6 + include/rdma/rw.h | 7 +- net/sunrpc/xprtrdma/svc_rdma_rw.c | 6 +- 24 files changed, 1291 insertions(+), 95 deletions(-) create mode 100644 drivers/pci/p2p.c create mode 100644 include/linux/pci-p2p.h -- 2.11.0 _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm
