[PATCH v3 0/3] create sysfs representation of ACPI HMAT

[Ross Zwisler]

This is the third revision of my patches adding a sysfs representation
of the ACPI Heterogeneous Memory Attribute Table (HMAT).  These patches
are based on v4.15-rc3 and a working tree can be found here:

https://git.kernel.org/pub/scm/linux/kernel/git/zwisler/linux.git/log/?h=hmat_v3

My goal is to get these patches merged for v4.16.

Changes from previous version (https://lkml.org/lkml/2017/7/6/749):

 - Changed "HMEM" to "HMAT" and "hmem" to "hmat" throughout to make sure
   that this effort doesn't get confused with Jerome's HMM work and to
   make it clear that this enabling is tightly tied to the ACPI HMAT
   table.  (John Hubbard)

 - Moved the link in the initiator (i.e. mem_init0/mem_tgt2) from
   pointing to the "mem_tgt2/local_init" attribute group to instead
   point at the mem_tgt2 target itself.  (Brice Goglin)

 - Simplified the contents of both the initiators and the targets so
   that we just symlink to the NUMA node and don't duplicate
   information.  For initiators this means that we no longer enumerate
   CPUs, and for targets this means that we don't provide physical
   address start and length information.  All of this is already
   available in the NUMA node directory itself (i.e.
   /sys/devices/system/node/node0), and it already accounts for the fact
   that both multiple CPUs and multiple memory regions can be owned by a
   given NUMA node.  Also removed some extra attributes (is_enabled,
   is_isolated) which I don't think are useful at this point in time.

I have tested this against many different configs that I implemented
using qemu.

---

==== Quick Summary ====

Platforms exist today which have multiple types of memory attached to a
single CPU.  These disparate memory ranges 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/local_init/read_bw_MBps:40960
  mem_tgt2/local_init/read_lat_nsec:50
  mem_tgt2/local_init/write_bw_MBps:40960
  mem_tgt2/local_init/write_lat_nsec:50

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.

==== Lots of Details ====

This patch set provides a sysfs representation of parts of the
Heterogeneous Memory Attribute Table (HMAT), 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 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 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.

Ross Zwisler (3):
  acpi: HMAT support in acpi_parse_entries_array()
  hmat: add heterogeneous memory sysfs support
  hmat: add performance attributes

 MAINTAINERS                         |   6 +
 drivers/acpi/Kconfig                |   1 +
 drivers/acpi/Makefile               |   1 +
 drivers/acpi/hmat/Kconfig           |   7 +
 drivers/acpi/hmat/Makefile          |   2 +
 drivers/acpi/hmat/core.c            | 797 ++++++++++++++++++++++++++++++++++++
 drivers/acpi/hmat/hmat.h            |  64 +++
 drivers/acpi/hmat/initiator.c       |  43 ++
 drivers/acpi/hmat/perf_attributes.c |  56 +++
 drivers/acpi/hmat/target.c          |  55 +++
 drivers/acpi/tables.c               |  52 ++-
 11 files changed, 1073 insertions(+), 11 deletions(-)
 create mode 100644 drivers/acpi/hmat/Kconfig
 create mode 100644 drivers/acpi/hmat/Makefile
 create mode 100644 drivers/acpi/hmat/core.c
 create mode 100644 drivers/acpi/hmat/hmat.h
 create mode 100644 drivers/acpi/hmat/initiator.c
 create mode 100644 drivers/acpi/hmat/perf_attributes.c
 create mode 100644 drivers/acpi/hmat/target.c

-- 
2.14.3