CpuId is a package for the Julia programming language that enables you to
query the availability of specific CPU features with low run-time cost
using the assembly instruction cpuid
.
Status: considered a pre-beta version, ready for you to try out.
Works on Julia 0.7 or newer, on Linux, Mac and Windows with Intel CPUs; AMD CPUs partially supported respectively support is in preparation.
Besides the obvious reason to gather information for diagnostics, the CPU provides valuable information when aiming at increasing the efficiency of code. Such use-cases could be to tailor the size of working sets of data according to the available cache sizes, to detect when the code is executed in a virtual machine (hypervisor), or to determine the size of the largest SIMD registers available to choose the best algorithm for the current hardware.
This information is obtained by directly querying the CPU through the cpuid
assembly instruction which operates only using CPU registers, and provides
a portable way to adapt code to specific hardware.
Same information may of course be collected from various sources, from Julia
itself or from the operating system, e.g. on Linux from /proc/cpuinfo
. See
below for a few alternatives. However, the cpuid
instruction
is portable in the sense that it doesn't rely on other external dependencies.
The full documentation is found in Intel's 4670 page combined Architectures
Software Devleoper Manual.
A more practical and concise overview of the cpuid
instruction is found at
sandpile.org.
CpuId is a registered Julia package; use the package manager to install:
Julia> Pkg.add("CpuId")
Or, if you're keen to get some intermediate updates, clone from GitHub master branch:
Julia> Pkg.clone("https://github.com/m-j-w/CpuId.jl")
See the diagnostic summary on your CPU by typing
julia> using CpuId
julia> cpuinfo()
Cpu Property Value
╾───────────────────╌───────────────────────────────────────────────────────────╼
Brand Intel(R) Xeon(R) CPU E3-1225 v5 @ 3.30GHz
Vendor :Intel
Architecture :Skylake
Model Family: 6, Model: 94, Stepping: 3, Type: 0
Cores 4 physical cores, 4 logical cores (on executing CPU)
No Hyperthreading detected
Clock Frequencies 3300 / 3700 MHz (base/max), 100 MHz bus
Data Cache Level 1:3 : (32, 256, 8192) kbytes
64 byte cache line size
Address Size 48 bits virtual, 39 bits physical
SIMD 256 bit = 32 byte max. SIMD vector size
Time Stamp Counter TSC is accessible via `rdtsc`
TSC runs at constant rate (invariant from clock frequency)
Perf. Monitoring Performance Monitoring Counters (PMC) revision 4
Available hardware counters per logical core:
3 fixed-function counters of 48 bit width
8 general-purpose counters of 48 bit width
Hypervisor No
Or get a list of the feature flags of your CPU with
julia> cpufeaturetable()
Cpu Feature Description
╾────────────╌───────────────────────────────────────────────────────────────╼
3DNowP 3D Now PREFETCH and PREFETCHW instructions
ACPI Thermal monitor and software controlled clock facilities (MSR)
ADX Intel ADX (Multi-Precision Add-Carry Instruction Extensions)
AES AES encryption instruction set
AHF64 LAHF and SAHF in PM64
APIC APIC on-chip (Advanced Programmable Interrupt Controller)
AVX 256bit Advanced Vector Extensions, AVX
AVX2 SIMD 256bit Advanced Vector Extensions 2
BMI1 Bit Manipulation Instruction Set 1
BMI2 Bit Manipulation Instruction Set 2
CLFLUSH CLFLUSHOPT Instructions
CLFSH CLFLUSH instruction (SSE2)
CMOV Conditional move CMOV and FCMOV instructions
CX16 CMPXCHG16B instruction
CX8 CMPXCHG8 instruction (64bit compare and exchange)
...
This release covers a selection of fundamental and higher level functionality:
cpuinfo()
generates the summary shown above (markdown string).cpubrand()
,cpumodel()
,cpuvendor()
allow the identification of the CPU.cpuarchitecture()
tries to infer the microarchitecture, currently only of Intel CPUs.cpucores()
andcputhreads()
to determine the number of physical and logical cores on the currently executing CPU, which typically share L3 caches and main memory bandwidth. If the result of both functions is equal, then the CPU does not use of hyperthreading.address_size()
andphysical_address_size()
return the number of bits used in pointers. Useful when stealing a few bits from a pointer.cachelinesize()
gives the size in bytes of one cache line, which is typically 64 bytes.cachesize()
returns a tuple with the sizes of the data caches in bytes.cpu_base_frequency()
,cpu_max_frequency()
,cpu_bus_frequency()
give - if supported by the CPU, the base, maximum and bus clock frequencies. Usehas_cpu_frequencies()
to check whether this property is supported.hypervised()
returns true when the CPU indicates that a hypervisor is running the operating system, aka a virtual machine. In that case,hvvendor()
may be invoked to get the, well, hypervisor vendor, andhvversion()
returns a dictionary of additional version tags.hvinfo()
generates a markdown summary of same dictionary.simdbits()
andsimdbytes()
return the size of the largest SIMD register available on the executing CPU.perf_revision()
to query the revision number of hardware performance monitoring counters, along withperf_fix_counters()
,perf_gen_counters()
,perf_fix_bits()
,perf_gen_bits()
to determine the number and bit width of available fixed-function and general purpose counters per logical core.cpucycle()
andcpucycle_id()
let you directly get the CPU's time stamp counter, which is increased for every CPU clock cycle. This is a method to perform low overhead micro-benchmarking; though, technically, this uses therdtsc
andrdtscp
instructions rather thancpuid
.cpufeature(::Symbol)
permits asking for the availability of a specific feature, andcpufeaturetable()
gives a complete overview of all detected features with a brief explanation, as shown above.
The cpuid
instruction is a generic way provided by the CPU vendor to obtain
basic hardware information. It provides data in form of boolean bit fields,
integer fields and strings, all packed in the returned CPU registers EAX, EBX,
ECX and EDX. Which information is returned is determined by the so called leaf,
which is defined by setting the input register EAX to a specific 32 bit integer
value before executing the instruction. The extent and kind of information
obtainable via this instruction has changed quite a lot over the past decade and
still evolves with every CPU generation. Thus, not all information is available
on every CPU model, and certainly everything is vendor dependent.
This Julia package also provides the cpucycle()
function which allows getting
the current time stamp counter (TSC) by emitting a rdtsc
instruction.
Similarly to cpuid
, it only requires CPU registers and is usable in user-land
code and facilitates an alternative approach to micro-benchmarking.
The behaviour on non-Intel CPUs is currently unknown; though technically a crash
of Julia could be expected, theoretically, a rather large list of CPUs support
the cpuid
instruction. Tip: Just try it and report back.
There are plenty of different CPUs, and in particular the cpuid
instruction
has numerous corner cases, which this package does not address, yet.
Moreover, the cpuid
instruction can only provide information for the executing
physical CPU, called a package. To obtain information on all packages, and all
physical and logical cores, the executing program must be pinned sequentially to
each and every core, and gather its properties. This is how libuv
, hwloc
or
the operating system obtain that kind information. However, this would require
additional external or operating system dependent code which is not the scope of
this package.
-
Why aren't all infos available that are seen e.g. in
/proc/cpuinfo
? Many of those features, flags and properties reside in the so called machine specific registers (MSR), which are only accessible to privileged programs running in the so called ring 0, such as the Linux kernel itself. Thus, short answer: You're not allowed to. -
The results obtained by
CpuId
functions are inconsistent with my hardware! Try other programs whether they give the same information or differ. If they differ, then you found a bug. See below for some alternatives, in particular the Linux command line tool cpuid. -
When running a hypervisor (virtual machine) the presented information is wrong! Hypervisor vendors are free to provide the
cpuid
information by intercepting calls to that instruction. Not all vendors comply, and some even permit the user to change what is reported. Thus, expect some surprises when a hypervisor is detected. -
My hypervisor is not detected! Either you're not really running a hypervisor, e.g. Bash on Windows is not a virtual machine, or there is a feature missing. Raise an issue on GitHub.
-
cpucycles()
invokesrdtsc
; that is notcpuid
! True. However, both are valuable when diagnosing performance issues and trying to perform micro benchmarks on specific hardware.
On Linux, most of the information may be obtained by reading from the /proc
tree, in particular /proc/cpuinfo
, which eventually also invokes the cpuid
instruction. Type man 4 cpuid
to get a brief description of this kernel
driver.
On many Linux distributions, there is also the command line tool cpuid, which essentially does exactly the same. On
Ubuntu, you would install it using sudo apt install cpuid
, then use it to show
a summary by simply typing cpuid
.
Then, of course, there are a few functions in Julia Base. These are
Base.Sys.cpu_info()
, and Base.Sys.cpu_summary()
, as well as the global
variables Base.Sys.CPU_CORES
, and Base.Sys.cpu_name
. These are mostly
provided by wrapping libuv. In particular CPU_CORES
is the reason for this
module: It's intrinsically unclear whether that number includes hyperthreading
cores, or whether it is referring to real physical cores of the current machine.
The Julia package Hwloc.jl provides similar and more information primarily directed towards the topology of your CPUs, viz. number of CPU packages, physical & logical cores and associated caches, along with a number of features to deal with thread affinity. However, it also pulls in additional external binary dependencies in that it relies on hwloc, which also implies quite some computational overhead. Whether this is an issue in the first place depends much on your use-case.
This Julia package CpuId is published as open source and licensed under the MIT "Expat" License.
Contributions welcome!
You're welcome to report successful usage or any issues via GitHub, and to open pull requests to extend the current functionality.