mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-24 21:24:00 +08:00
4f4cfa6c56
There are lots of documents that belong to the admin-guide but are on random places (most under Documentation root dir). Move them to the admin guide. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com> Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
226 lines
6.9 KiB
ReStructuredText
226 lines
6.9 KiB
ReStructuredText
.. 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.
|
|
|
|
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.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_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
|