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101 lines
3.8 KiB
101 lines
3.8 KiB
=========================================== |
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How CPU topology info is exported via sysfs |
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CPU topology info is exported via sysfs. Items (attributes) are similar |
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to /proc/cpuinfo output of some architectures. They reside in |
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/sys/devices/system/cpu/cpuX/topology/. Please refer to the ABI file: |
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Documentation/ABI/stable/sysfs-devices-system-cpu. |
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Architecture-neutral, drivers/base/topology.c, exports these attributes. |
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However the die, cluster, book, and drawer hierarchy related sysfs files will |
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only be created if an architecture provides the related macros as described |
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below. |
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For an architecture to support this feature, it must define some of |
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these macros in include/asm-XXX/topology.h:: |
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#define topology_physical_package_id(cpu) |
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#define topology_die_id(cpu) |
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#define topology_cluster_id(cpu) |
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#define topology_core_id(cpu) |
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#define topology_book_id(cpu) |
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#define topology_drawer_id(cpu) |
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#define topology_sibling_cpumask(cpu) |
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#define topology_core_cpumask(cpu) |
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#define topology_cluster_cpumask(cpu) |
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#define topology_die_cpumask(cpu) |
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#define topology_book_cpumask(cpu) |
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#define topology_drawer_cpumask(cpu) |
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The type of ``**_id macros`` is int. |
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The type of ``**_cpumask macros`` is ``(const) struct cpumask *``. The latter |
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correspond with appropriate ``**_siblings`` sysfs attributes (except for |
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topology_sibling_cpumask() which corresponds with thread_siblings). |
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To be consistent on all architectures, include/linux/topology.h |
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provides default definitions for any of the above macros that are |
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not defined by include/asm-XXX/topology.h: |
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1) topology_physical_package_id: -1 |
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2) topology_die_id: -1 |
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3) topology_cluster_id: -1 |
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4) topology_core_id: 0 |
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5) topology_book_id: -1 |
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6) topology_drawer_id: -1 |
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7) topology_sibling_cpumask: just the given CPU |
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8) topology_core_cpumask: just the given CPU |
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9) topology_cluster_cpumask: just the given CPU |
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10) topology_die_cpumask: just the given CPU |
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11) topology_book_cpumask: just the given CPU |
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12) topology_drawer_cpumask: just the given CPU |
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Additionally, CPU topology information is provided under |
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/sys/devices/system/cpu and includes these files. The internal |
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source for the output is in brackets ("[]"). |
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=========== ========================================================== |
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kernel_max: the maximum CPU index allowed by the kernel configuration. |
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[NR_CPUS-1] |
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offline: CPUs that are not online because they have been |
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HOTPLUGGED off or exceed the limit of CPUs allowed by the |
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kernel configuration (kernel_max above). |
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[~cpu_online_mask + cpus >= NR_CPUS] |
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online: CPUs that are online and being scheduled [cpu_online_mask] |
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possible: CPUs that have been allocated resources and can be |
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brought online if they are present. [cpu_possible_mask] |
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present: CPUs that have been identified as being present in the |
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system. [cpu_present_mask] |
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=========== ========================================================== |
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The format for the above output is compatible with cpulist_parse() |
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[see <linux/cpumask.h>]. Some examples follow. |
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In this example, there are 64 CPUs in the system but cpus 32-63 exceed |
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the kernel max which is limited to 0..31 by the NR_CPUS config option |
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being 32. Note also that CPUs 2 and 4-31 are not online but could be |
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brought online as they are both present and possible:: |
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kernel_max: 31 |
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offline: 2,4-31,32-63 |
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online: 0-1,3 |
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possible: 0-31 |
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present: 0-31 |
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In this example, the NR_CPUS config option is 128, but the kernel was |
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started with possible_cpus=144. There are 4 CPUs in the system and cpu2 |
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was manually taken offline (and is the only CPU that can be brought |
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online.):: |
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kernel_max: 127 |
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offline: 2,4-127,128-143 |
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online: 0-1,3 |
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possible: 0-127 |
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present: 0-3 |
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See Documentation/core-api/cpu_hotplug.rst for the possible_cpus=NUM |
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kernel start parameter as well as more information on the various cpumasks.
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