A memory tiering abstract distance calculation algorithm based on ACPI
HMAT is implemented.  The basic idea is as follows.

The performance attributes of system default DRAM nodes are recorded as
the base line.  Whose abstract distance is MEMTIER_ADISTANCE_DRAM.  Then,
the ratio of the abstract distance of a memory node (target) to
MEMTIER_ADISTANCE_DRAM is scaled based on the ratio of the performance
attributes of the node to that of the default DRAM nodes.

The functions to record the read/write latency/bandwidth of the default
DRAM nodes and calculate abstract distance according to read/write
latency/bandwidth ratio will be used by CXL CDAT (Coherent Device
Attribute Table) and other memory device drivers.  So, they are put in
memory-tiers.c.

Link: https://lkml.kernel.org/r/20230926060628.265989-4-ying.huang@intel.comSigned-off-by: "Huang, Ying" <ying.huang@intel.com>
Tested-by: Bharata B Rao <bharata@amd.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Rafael J Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>