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linux/Documentation/ABI/testing/sysfs-devices-system-cpu
Steve Capper f8d9f92452 arm64: cpuinfo: Expose MIDR_EL1 and REVIDR_EL1 to sysfs 
It can be useful for JIT software to be aware of MIDR_EL1 and
REVIDR_EL1 to ascertain the presence of any core errata that could
affect code generation.

This patch exposes these registers through sysfs:

/sys/devices/system/cpu/cpu$ID/regs/identification/midr_el1
/sys/devices/system/cpu/cpu$ID/regs/identification/revidr_el1

where $ID is the cpu number. For big.LITTLE systems, one can have a
mixture of cores (e.g. Cortex A53 and Cortex A57), thus all CPUs need
to be enumerated.

If the kernel does not have valid information to populate these entries
with, an empty string is returned to userspace.

Cc: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Steve Capper <steve.capper@linaro.org>
[suzuki.poulose@arm.com: ABI documentation updates, hotplug notifiers, kobject changes]
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2016-07-12 16:09:37 +01:00

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What: /sys/devices/system/cpu/
Date: pre-git history
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description:
A collection of both global and individual CPU attributes
Individual CPU attributes are contained in subdirectories
named by the kernel's logical CPU number, e.g.:
/sys/devices/system/cpu/cpu#/
What: /sys/devices/system/cpu/kernel_max
/sys/devices/system/cpu/offline
/sys/devices/system/cpu/online
/sys/devices/system/cpu/possible
/sys/devices/system/cpu/present
Date: December 2008
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: CPU topology files that describe kernel limits related to
hotplug. Briefly:
kernel_max: the maximum cpu index allowed by the kernel
configuration.
offline: cpus that are not online because they have been
HOTPLUGGED off or exceed the limit of cpus allowed by the
kernel configuration (kernel_max above).
online: cpus that are online and being scheduled.
possible: cpus that have been allocated resources and can be
brought online if they are present.
present: cpus that have been identified as being present in
the system.
See Documentation/cputopology.txt for more information.
What: /sys/devices/system/cpu/probe
/sys/devices/system/cpu/release
Date: November 2009
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Dynamic addition and removal of CPU's. This is not hotplug
removal, this is meant complete removal/addition of the CPU
from the system.
probe: writes to this file will dynamically add a CPU to the
system. Information written to the file to add CPU's is
architecture specific.
release: writes to this file dynamically remove a CPU from
the system. Information writtento the file to remove CPU's
is architecture specific.
What: /sys/devices/system/cpu/cpu#/node
Date: October 2009
Contact: Linux memory management mailing list <linux-mm@kvack.org>
Description: Discover NUMA node a CPU belongs to
When CONFIG_NUMA is enabled, a symbolic link that points
to the corresponding NUMA node directory.
For example, the following symlink is created for cpu42
in NUMA node 2:
/sys/devices/system/cpu/cpu42/node2 -> ../../node/node2
What: /sys/devices/system/cpu/cpu#/topology/core_id
/sys/devices/system/cpu/cpu#/topology/core_siblings
/sys/devices/system/cpu/cpu#/topology/core_siblings_list
/sys/devices/system/cpu/cpu#/topology/physical_package_id
/sys/devices/system/cpu/cpu#/topology/thread_siblings
/sys/devices/system/cpu/cpu#/topology/thread_siblings_list
Date: December 2008
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: CPU topology files that describe a logical CPU's relationship
to other cores and threads in the same physical package.
One cpu# directory is created per logical CPU in the system,
e.g. /sys/devices/system/cpu/cpu42/.
Briefly, the files above are:
core_id: the CPU core ID of cpu#. Typically it is the
hardware platform's identifier (rather than the kernel's).
The actual value is architecture and platform dependent.
core_siblings: internal kernel map of cpu#'s hardware threads
within the same physical_package_id.
core_siblings_list: human-readable list of the logical CPU
numbers within the same physical_package_id as cpu#.
physical_package_id: physical package id of cpu#. Typically
corresponds to a physical socket number, but the actual value
is architecture and platform dependent.
thread_siblings: internel kernel map of cpu#'s hardware
threads within the same core as cpu#
thread_siblings_list: human-readable list of cpu#'s hardware
threads within the same core as cpu#
See Documentation/cputopology.txt for more information.
What: /sys/devices/system/cpu/cpuidle/current_driver
/sys/devices/system/cpu/cpuidle/current_governer_ro
Date: September 2007
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Discover cpuidle policy and mechanism
Various CPUs today support multiple idle levels that are
differentiated by varying exit latencies and power
consumption during idle.
Idle policy (governor) is differentiated from idle mechanism
(driver)
current_driver: displays current idle mechanism
current_governor_ro: displays current idle policy
See files in Documentation/cpuidle/ for more information.
What: /sys/devices/system/cpu/cpu#/cpufreq/*
Date: pre-git history
Contact: linux-pm@vger.kernel.org
Description: Discover and change clock speed of CPUs
Clock scaling allows you to change the clock speed of the
CPUs on the fly. This is a nice method to save battery
power, because the lower the clock speed, the less power
the CPU consumes.
There are many knobs to tweak in this directory.
See files in Documentation/cpu-freq/ for more information.
In particular, read Documentation/cpu-freq/user-guide.txt
to learn how to control the knobs.
What: /sys/devices/system/cpu/cpu#/cpufreq/freqdomain_cpus
Date: June 2013
Contact: linux-pm@vger.kernel.org
Description: Discover CPUs in the same CPU frequency coordination domain
freqdomain_cpus is the list of CPUs (online+offline) that share
the same clock/freq domain (possibly at the hardware level).
That information may be hidden from the cpufreq core and the
value of related_cpus may be different from freqdomain_cpus. This
attribute is useful for user space DVFS controllers to get better
power/performance results for platforms using acpi-cpufreq.
This file is only present if the acpi-cpufreq driver is in use.
What: /sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
Date: August 2008
KernelVersion: 2.6.27
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Disable L3 cache indices
These files exist in every CPU's cache/index3 directory. Each
cache_disable_{0,1} file corresponds to one disable slot which
can be used to disable a cache index. Reading from these files
on a processor with this functionality will return the currently
disabled index for that node. There is one L3 structure per
node, or per internal node on MCM machines. Writing a valid
index to one of these files will cause the specificed cache
index to be disabled.
All AMD processors with L3 caches provide this functionality.
For details, see BKDGs at
http://developer.amd.com/documentation/guides/Pages/default.aspx
What: /sys/devices/system/cpu/cpufreq/boost
Date: August 2012
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Processor frequency boosting control
This switch controls the boost setting for the whole system.
Boosting allows the CPU and the firmware to run at a frequency
beyound it's nominal limit.
More details can be found in Documentation/cpu-freq/boost.txt
What: /sys/devices/system/cpu/cpu#/crash_notes
/sys/devices/system/cpu/cpu#/crash_notes_size
Date: April 2013
Contact: kexec@lists.infradead.org
Description: address and size of the percpu note.
crash_notes: the physical address of the memory that holds the
note of cpu#.
crash_notes_size: size of the note of cpu#.
What: /sys/devices/system/cpu/intel_pstate/max_perf_pct
/sys/devices/system/cpu/intel_pstate/min_perf_pct
/sys/devices/system/cpu/intel_pstate/no_turbo
Date: February 2013
Contact: linux-pm@vger.kernel.org
Description: Parameters for the Intel P-state driver
Logic for selecting the current P-state in Intel
Sandybridge+ processors. The three knobs control
limits for the P-state that will be requested by the
driver.
max_perf_pct: limits the maximum P state that will be requested by
the driver stated as a percentage of the available performance.
min_perf_pct: limits the minimum P state that will be requested by
the driver stated as a percentage of the available performance.
no_turbo: limits the driver to selecting P states below the turbo
frequency range.
More details can be found in Documentation/cpu-freq/intel-pstate.txt
What: /sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below>
Date: July 2014(documented, existed before August 2008)
Contact: Sudeep Holla <sudeep.holla@arm.com>
Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Parameters for the CPU cache attributes
allocation_policy:
- WriteAllocate: allocate a memory location to a cache line
on a cache miss because of a write
- ReadAllocate: allocate a memory location to a cache line
on a cache miss because of a read
- ReadWriteAllocate: both writeallocate and readallocate
attributes: LEGACY used only on IA64 and is same as write_policy
coherency_line_size: the minimum amount of data in bytes that gets
transferred from memory to cache
level: the cache hierarchy in the multi-level cache configuration
number_of_sets: total number of sets in the cache, a set is a
collection of cache lines with the same cache index
physical_line_partition: number of physical cache line per cache tag
shared_cpu_list: the list of logical cpus sharing the cache
shared_cpu_map: logical cpu mask containing the list of cpus sharing
the cache
size: the total cache size in kB
type:
- Instruction: cache that only holds instructions
- Data: cache that only caches data
- Unified: cache that holds both data and instructions
ways_of_associativity: degree of freedom in placing a particular block
of memory in the cache
write_policy:
- WriteThrough: data is written to both the cache line
and to the block in the lower-level memory
- WriteBack: data is written only to the cache line and
the modified cache line is written to main
memory only when it is replaced
What: /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/turbo_stat
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/sub_turbo_stat
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/unthrottle
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/powercap
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overtemp
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/supply_fault
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overcurrent
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/occ_reset
Date: March 2016
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
Description: POWERNV CPUFreq driver's frequency throttle stats directory and
attributes
'cpuX/cpufreq/throttle_stats' directory contains the CPU frequency
throttle stat attributes for the chip. The throttle stats of a cpu
is common across all the cpus belonging to a chip. Below are the
throttle attributes exported in the 'throttle_stats' directory:
- turbo_stat : This file gives the total number of times the max
frequency is throttled to lower frequency in turbo (at and above
nominal frequency) range of frequencies.
- sub_turbo_stat : This file gives the total number of times the
max frequency is throttled to lower frequency in sub-turbo(below
nominal frequency) range of frequencies.
- unthrottle : This file gives the total number of times the max
frequency is unthrottled after being throttled.
- powercap : This file gives the total number of times the max
frequency is throttled due to 'Power Capping'.
- overtemp : This file gives the total number of times the max
frequency is throttled due to 'CPU Over Temperature'.
- supply_fault : This file gives the total number of times the
max frequency is throttled due to 'Power Supply Failure'.
- overcurrent : This file gives the total number of times the
max frequency is throttled due to 'Overcurrent'.
- occ_reset : This file gives the total number of times the max
frequency is throttled due to 'OCC Reset'.
The sysfs attributes representing different throttle reasons like
powercap, overtemp, supply_fault, overcurrent and occ_reset map to
the reasons provided by OCC firmware for throttling the frequency.
What: /sys/devices/system/cpu/cpufreq/policyX/throttle_stats
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/turbo_stat
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/sub_turbo_stat
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/unthrottle
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/powercap
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overtemp
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/supply_fault
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overcurrent
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/occ_reset
Date: March 2016
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
Description: POWERNV CPUFreq driver's frequency throttle stats directory and
attributes
'policyX/throttle_stats' directory and all the attributes are same as
the /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats directory and
attributes which give the frequency throttle information of the chip.
What: /sys/devices/system/cpu/cpuX/regs/
/sys/devices/system/cpu/cpuX/regs/identification/
/sys/devices/system/cpu/cpuX/regs/identification/midr_el1
/sys/devices/system/cpu/cpuX/regs/identification/revidr_el1
Date: June 2016
Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
Description: AArch64 CPU registers
'identification' directory exposes the CPU ID registers for
identifying model and revision of the CPU.
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