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diff --git a/Documentation/x86/topology.txt b/Documentation/x86/topology.txt deleted file mode 100644 index 2953e3ec9a02..000000000000 --- a/Documentation/x86/topology.txt +++ /dev/null @@ -1,217 +0,0 @@ -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/cputopology.txt. 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. - - 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.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. - - - cpuinfo_x86.logical_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 |