On Thu, 2017-07-06 at 15:52 -0600, Ross Zwisler wrote: > ==== 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 Could you please explain these charactersitics, are they in the patches to follow? > 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 > How to these numbers compare to normal system memory? > 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. Could you expand on proximity domains, are they the same as node distance or is this ACPI terminology for something more? > > 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. > Balbir Singh. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
