==== Quick Summary ==== Platforms in the very near future will have multiple types of memory attached to a single CPU. These disparate memory ranges will have some characteristics in common, such as CPU cache coherence, but they can have wide ranges of performance both in terms of latency and bandwidth. For example, consider a system that contains persistent memory, standard DDR memory and High Bandwidth Memory (HBM), all attached to the same CPU. There could potentially be an order of magnitude or more difference in performance between the slowest and fastest memory attached to that CPU. With the current Linux code NUMA nodes are CPU-centric, so all the memory attached to a given CPU will be lumped into the same NUMA node. This makes it very difficult for userspace applications to understand the performance of different memory ranges on a given CPU. We solve this issue by providing userspace with performance information on individual memory ranges. This performance information is exposed via sysfs: # grep . mem_tgt2/* mem_tgt2/local_init/* 2>/dev/null mem_tgt2/firmware_id:1 mem_tgt2/is_cached:0 mem_tgt2/is_enabled:1 mem_tgt2/is_isolated:0 mem_tgt2/phys_addr_base:0x0 mem_tgt2/phys_length_bytes:0x800000000 mem_tgt2/local_init/read_bw_MBps:30720 mem_tgt2/local_init/read_lat_nsec:100 mem_tgt2/local_init/write_bw_MBps:30720 mem_tgt2/local_init/write_lat_nsec:100 This allows applications to easily find the memory that they want to use. We expect that the existing NUMA APIs will be enhanced to use this new information so that applications can continue to use them to select their desired memory. This series is built upon acpica-1705: https://github.com/zetalog/linux/commits/acpica-1705 And you can find a working tree here: https://git.kernel.org/pub/scm/linux/kernel/git/zwisler/linux.git/log/?h=hmem_sysfs ==== Lots of Details ==== This patch set is only concerned with CPU-addressable memory types, not on-device memory like what we have with Jerome Glisse's HMM series: https://lwn.net/Articles/726691/ This patch set works by enabling the new Heterogeneous Memory Attribute Table (HMAT) table, newly defined in ACPI 6.2. One major conceptual change in ACPI 6.2 related to this work is that proximity domains no longer need to contain a processor. We can now have memory-only proximity domains, which means that we can now have memory-only Linux NUMA nodes. Here is an example configuration where we have a single processor, one range of regular memory and one range of HBM: +---------------+ +----------------+ | Processor | | Memory | | prox domain 0 +---+ prox domain 1 | | NUMA node 1 | | NUMA node 2 | +-------+-------+ +----------------+ | +-------+----------+ | HBM | | prox domain 2 | | NUMA node 0 | +------------------+ This gives us one initiator (the processor) and two targets (the two memory ranges). Each of these three has its own ACPI proximity domain and associated Linux NUMA node. Note also that while there is a 1:1 mapping from each proximity domain to each NUMA node, the numbers don't necessarily match up. Additionally we can have extra NUMA nodes that don't map back to ACPI proximity domains. The above configuration could also have the processor and one of the two memory ranges sharing a proximity domain and NUMA node, but for the purposes of the HMAT the two memory ranges will always need to be separated. The overall goal of this series and of the HMAT is to allow users to identify memory using its performance characteristics. This can broadly be done in one of two ways: Option 1: Provide the user with a way to map between proximity domains and NUMA nodes and a way to access the HMAT directly (probably via /sys/firmware/acpi/tables). Then, through possibly a library and a daemon, provide an API so that applications can either request information about memory ranges, or request memory allocations that meet a given set of performance characteristics. Option 2: Provide the user with HMAT performance data directly in sysfs, allowing applications to directly access it without the need for the library and daemon. The kernel work for option 1 is started by patches 1-3. These just surface the minimal amount of information in sysfs to allow userspace to map between proximity domains and NUMA nodes so that the raw data in the HMAT table can be understood. Patches 4 and 5 enable option 2, adding performance information from the HMAT to sysfs. The second option is complicated by the amount of HMAT data that could be present in very large systems, so in this series we only surface performance information for local (initiator,target) pairings. The changelog for patch 5 discusses this in detail. The naming collision between Jerome's "Heterogeneous Memory Management (HMM)" and this "Heterogeneous Memory (HMEM)" series is unfortunate, but I was trying to stick with the word "Heterogeneous" because of the naming of the ACPI 6.2 Heterogeneous Memory Attribute Table table. Suggestions for better naming are welcome. ==== Next steps ==== There is still a lot of work to be done on this series, but the overall goal of this RFC is to gather feedback on which of the two options we should pursue, or whether some third option is preferred. After that is done and we have a solid direction we can add support for ACPI hot add, test more complex configurations, etc. So, for applications that need to differentiate between memory ranges based on their performance, what option would work best for you? Is the local (initiator,target) performance provided by patch 5 enough, or do you require performance information for all possible (initiator,target) pairings? If option 1 looks best, do we have ideas on what the userspace API would look like? What other things should we consider, or what needs do you have that aren't being addressed? --- Changes from previous RFC (https://lwn.net/Articles/724562/): - Allow multiple initiators to be local to a given memory target, as long as they all have the same performance characteristics. (Dan Williams) - A few small fixes to the ACPI parsing to allow for configurations I hadn't previously considered. Ross Zwisler (5): acpi: add missing include in acpi_numa.h acpi: HMAT support in acpi_parse_entries_array() hmem: add heterogeneous memory sysfs support sysfs: add sysfs_add_group_link() hmem: add performance attributes MAINTAINERS | 5 + drivers/acpi/Kconfig | 1 + drivers/acpi/Makefile | 1 + drivers/acpi/hmem/Kconfig | 7 + drivers/acpi/hmem/Makefile | 2 + drivers/acpi/hmem/core.c | 835 ++++++++++++++++++++++++++++++++++++ drivers/acpi/hmem/hmem.h | 64 +++ drivers/acpi/hmem/initiator.c | 61 +++ drivers/acpi/hmem/perf_attributes.c | 56 +++ drivers/acpi/hmem/target.c | 97 +++++ drivers/acpi/numa.c | 2 +- drivers/acpi/tables.c | 52 ++- fs/sysfs/group.c | 30 +- include/acpi/acpi_numa.h | 1 + include/linux/sysfs.h | 2 + 15 files changed, 1197 insertions(+), 19 deletions(-) create mode 100644 drivers/acpi/hmem/Kconfig create mode 100644 drivers/acpi/hmem/Makefile create mode 100644 drivers/acpi/hmem/core.c create mode 100644 drivers/acpi/hmem/hmem.h create mode 100644 drivers/acpi/hmem/initiator.c create mode 100644 drivers/acpi/hmem/perf_attributes.c create mode 100644 drivers/acpi/hmem/target.c -- 2.9.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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