Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. SPDX-License-Identifier: GPL-2.0
+
+============
+x86 Topology
+============
+
+This documents and clarifies the main aspects of x86 topology modelling and
+representation in the kernel. Update/change when doing changes to the
+respective code.
+
+The architecture-agnostic topology definitions are in
+Documentation/admin-guide/cputopology.rst. This file holds x86-specific
+differences/specialities which must not necessarily apply to the generic
+definitions. Thus, the way to read up on Linux topology on x86 is to start
+with the generic one and look at this one in parallel for the x86 specifics.
+
+Needless to say, code should use the generic functions - this file is *only*
+here to *document* the inner workings of x86 topology.
+
+Started by Thomas Gleixner <tglx@linutronix.de> and Borislav Petkov <bp@alien8.de>.
+
+The main aim of the topology facilities is to present adequate interfaces to
+code which needs to know/query/use the structure of the running system wrt
+threads, cores, packages, etc.
+
+The kernel does not care about the concept of physical sockets because a
+socket has no relevance to software. It's an electromechanical component. In
+the past a socket always contained a single package (see below), but with the
+advent of Multi Chip Modules (MCM) a socket can hold more than one package. So
+there might be still references to sockets in the code, but they are of
+historical nature and should be cleaned up.
+
+The topology of a system is described in the units of:
+
+    - packages
+    - cores
+    - threads
+
+Package
+=======
+Packages contain a number of cores plus shared resources, e.g. DRAM
+controller, shared caches etc.
+
+Modern systems may also use the term 'Die' for package.
+
+AMD nomenclature for package is 'Node'.
+
+Package-related topology information in the kernel:
+
+  - cpuinfo_x86.x86_max_cores:
+
+    The number of cores in a package. This information is retrieved via CPUID.
+
+  - cpuinfo_x86.x86_max_dies:
+
+    The number of dies in a package. This information is retrieved via CPUID.
+
+  - cpuinfo_x86.cpu_die_id:
+
+    The physical ID of the die. This information is retrieved via CPUID.
+
+  - cpuinfo_x86.phys_proc_id:
+
+    The physical ID of the package. This information is retrieved via CPUID
+    and deduced from the APIC IDs of the cores in the package.
+
+    Modern systems use this value for the socket. There may be multiple
+    packages within a socket. This value may differ from cpu_die_id.
+
+  - cpuinfo_x86.logical_proc_id:
+
+    The logical ID of the package. As we do not trust BIOSes to enumerate the
+    packages in a consistent way, we introduced the concept of logical package
+    ID so we can sanely calculate the number of maximum possible packages in
+    the system and have the packages enumerated linearly.
+
+  - topology_max_packages():
+
+    The maximum possible number of packages in the system. Helpful for per
+    package facilities to preallocate per package information.
+
+  - cpu_llc_id:
+
+    A per-CPU variable containing:
+
+      - On Intel, the first APIC ID of the list of CPUs sharing the Last Level
+        Cache
+
+      - On AMD, the Node ID or Core Complex ID containing the Last Level
+        Cache. In general, it is a number identifying an LLC uniquely on the
+        system.
+
+Cores
+=====
+A core consists of 1 or more threads. It does not matter whether the threads
+are SMT- or CMT-type threads.
+
+AMDs nomenclature for a CMT core is "Compute Unit". The kernel always uses
+"core".
+
+Core-related topology information in the kernel:
+
+  - smp_num_siblings:
+
+    The number of threads in a core. The number of threads in a package can be
+    calculated by::
+
+	threads_per_package = cpuinfo_x86.x86_max_cores * smp_num_siblings
+
+
+Threads
+=======
+A thread is a single scheduling unit. It's the equivalent to a logical Linux
+CPU.
+
+AMDs nomenclature for CMT threads is "Compute Unit Core". The kernel always
+uses "thread".
+
+Thread-related topology information in the kernel:
+
+  - topology_core_cpumask():
+
+    The cpumask contains all online threads in the package to which a thread
+    belongs.
+
+    The number of online threads is also printed in /proc/cpuinfo "siblings."
+
+  - topology_sibling_cpumask():
+
+    The cpumask contains all online threads in the core to which a thread
+    belongs.
+
+  - topology_logical_package_id():
+
+    The logical package ID to which a thread belongs.
+
+  - topology_physical_package_id():
+
+    The physical package ID to which a thread belongs.
+
+  - topology_core_id();
+
+    The ID of the core to which a thread belongs. It is also printed in /proc/cpuinfo
+    "core_id."
+
+
+
+System topology examples
+========================
+
+.. note::
+  The alternative Linux CPU enumeration depends on how the BIOS enumerates the
+  threads. Many BIOSes enumerate all threads 0 first and then all threads 1.
+  That has the "advantage" that the logical Linux CPU numbers of threads 0 stay
+  the same whether threads are enabled or not. That's merely an implementation
+  detail and has no practical impact.
+
+1) Single Package, Single Core::
+
+   [package 0] -> [core 0] -> [thread 0] -> Linux CPU 0
+
+2) Single Package, Dual Core
+
+   a) One thread per core::
+
+	[package 0] -> [core 0] -> [thread 0] -> Linux CPU 0
+		    -> [core 1] -> [thread 0] -> Linux CPU 1
+
+   b) Two threads per core::
+
+	[package 0] -> [core 0] -> [thread 0] -> Linux CPU 0
+				-> [thread 1] -> Linux CPU 1
+		    -> [core 1] -> [thread 0] -> Linux CPU 2
+				-> [thread 1] -> Linux CPU 3
+
+      Alternative enumeration::
+
+	[package 0] -> [core 0] -> [thread 0] -> Linux CPU 0
+				-> [thread 1] -> Linux CPU 2
+		    -> [core 1] -> [thread 0] -> Linux CPU 1
+				-> [thread 1] -> Linux CPU 3
+
+      AMD nomenclature for CMT systems::
+
+	[node 0] -> [Compute Unit 0] -> [Compute Unit Core 0] -> Linux CPU 0
+				     -> [Compute Unit Core 1] -> Linux CPU 1
+		 -> [Compute Unit 1] -> [Compute Unit Core 0] -> Linux CPU 2
+				     -> [Compute Unit Core 1] -> Linux CPU 3
+
+4) Dual Package, Dual Core
+
+   a) One thread per core::
+
+	[package 0] -> [core 0] -> [thread 0] -> Linux CPU 0
+		    -> [core 1] -> [thread 0] -> Linux CPU 1
+
+	[package 1] -> [core 0] -> [thread 0] -> Linux CPU 2
+		    -> [core 1] -> [thread 0] -> Linux CPU 3
+
+   b) Two threads per core::
+
+	[package 0] -> [core 0] -> [thread 0] -> Linux CPU 0
+				-> [thread 1] -> Linux CPU 1
+		    -> [core 1] -> [thread 0] -> Linux CPU 2
+				-> [thread 1] -> Linux CPU 3
+
+	[package 1] -> [core 0] -> [thread 0] -> Linux CPU 4
+				-> [thread 1] -> Linux CPU 5
+		    -> [core 1] -> [thread 0] -> Linux CPU 6
+				-> [thread 1] -> Linux CPU 7
+
+      Alternative enumeration::
+
+	[package 0] -> [core 0] -> [thread 0] -> Linux CPU 0
+				-> [thread 1] -> Linux CPU 4
+		    -> [core 1] -> [thread 0] -> Linux CPU 1
+				-> [thread 1] -> Linux CPU 5
+
+	[package 1] -> [core 0] -> [thread 0] -> Linux CPU 2
+				-> [thread 1] -> Linux CPU 6
+		    -> [core 1] -> [thread 0] -> Linux CPU 3
+				-> [thread 1] -> Linux CPU 7
+
+      AMD nomenclature for CMT systems::
+
+	[node 0] -> [Compute Unit 0] -> [Compute Unit Core 0] -> Linux CPU 0
+				     -> [Compute Unit Core 1] -> Linux CPU 1
+		 -> [Compute Unit 1] -> [Compute Unit Core 0] -> Linux CPU 2
+				     -> [Compute Unit Core 1] -> Linux CPU 3
+
+	[node 1] -> [Compute Unit 0] -> [Compute Unit Core 0] -> Linux CPU 4
+				     -> [Compute Unit Core 1] -> Linux CPU 5
+		 -> [Compute Unit 1] -> [Compute Unit Core 0] -> Linux CPU 6
+				     -> [Compute Unit Core 1] -> Linux CPU 7