gmx::HardwareTopology::Machine Struct Reference

#include <gromacs/hardware/hardwaretopology.h>

Collaboration diagram for gmx::HardwareTopology::Machine:

Description

Hardware topology information about the entire machine.

The machine structure is a tree with top-down information about all packages, cores, and processing units in the system. For example, an operating system logical processor index can be found as machine.packages[0].cores[2].processingUnits[1].osId. In some cases you might need the opposite lookup, i.e. the processing unit Id on the topology from the OS-assigned Id. This is present in the map osIdToPuId, provided we have sufficient support level.

It can happen that our process is only allowed to run on a subset of processors, e.g. because we are running in a container or because some cores are reserved for management, which complicates core detection a bit. In this case, the hardware topology will only list the PUs on which we are allowed to run, meaning it might look quite unbalanced.

First, remember that you must consider the supportLevel before using data in this class.

• If supportLevel is SupportLevel::None, we simply don't have any valid information - not even the number of logical processors.
• If we have at least SupportLevel::LogicalProcessorCount, we have detected the number of logical CPUs in the system, but we might not have any information whether we are allowed to run on all of them or not. To decide how many threads to start, always check the maxThreads() method, since we might have been able to detect that we are only allowed to run on a subset, e.g. when executing in a container environment where the machine has many cores, but the cpu limit for our container is low.
• If supportLevel is at least SupportLevel::Basic, we have valid topology information about packages, cores and processing units both in the tree-like structure starting with machine().packages, in the linear logicalProcessors vector, and the map osIdToPuId is also valid.
• If supportLevel is at least SupportLevel::Full, the cache and ccNUMA information is also valid.
• Finally, for SupportLevel::FullWithDevices, the device structure is valid in addition to everything else.

Note

Never use the size of the logicalProcessors vector to decide how many threads to start, but consult maxThreads().

If you use cpu sets or other ways to decide what processors to run on, such OS-provided functions always refer to the osId of the processing unit.

Public Attributes
std::vector< LogicalProcessor >	logicalProcessors
	Logical processing unit info, indexed by PU Ids in vector.
std::map< int, int >	osIdToPuId
	Map from OS to topology processing unit ids.
std::vector< Package >	packages
	All the packages in the system.
std::vector< Cache >	caches
	Caches in increasing level order.
Numa	numa
	Structure with all numa information.
std::vector< Device >	devices
	Devices on PCI bus.

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The documentation for this struct was generated from the following files:

• src/gromacs/hardware/hardwaretopology.h
• src/gromacs/hardware/hardwaretopology.cpp