Skip to contents

Is CPU energy measurable here?

Source: R/compute_footprint.R
rapl_available.Rd

TRUE when the operating system exposes readable RAPL (Running Average Power Limit) energy counters for at least one CPU package: Linux with the intel_rapl powercap driver (Intel and, since kernel 5.8, AMD), with read permission on energy_uj. On most systems since Linux 5.10 that file is readable by root only, so FALSE is the common answer for an ordinary user, and compute_footprint then falls back to its model.

Usage

rapl_available(rapl_dir = "/sys/class/powercap")

Arguments

rapl_dir

Character scalar, the powercap directory; default "/sys/class/powercap", the Linux location. Another path is useful for testing against a copy of the directory tree.

Value

A logical scalar: TRUE when every CPU-package energy counter under rapl_dir is readable, FALSE otherwise (including when the directory does not exist).

Details

A domain counts when it is a directory named intel-rapl:N (the intel-rapl:N:M subdomains are parts of a package and would count the same energy twice) whose name file starts with "package" and whose energy_uj file holds a number. Every such domain must be readable: if any is not, the answer is FALSE. Only files under rapl_dir are read; nothing is written. On macOS and Windows there is no such directory and the answer is FALSE. Errors when rapl_dir is not a single non-missing string.

See also

compute_footprint

Examples

rapl_available()
#> [1] FALSE

# a fake powercap tree with one readable package domain (Linux names the domain
# "intel-rapl:0"; a colon is not allowed in a Windows file name)
if (.Platform$OS.type != "windows") {
  d <- file.path(tempfile(), "intel-rapl:0")
  dir.create(d, recursive = TRUE)
  writeLines("package-0", file.path(d, "name"))
  writeLines("123456789", file.path(d, "energy_uj"))
  rapl_available(dirname(d))
}
#> [1] TRUE

# a folder that does not exist is simply FALSE; a non-path is an error
rapl_available(file.path(tempdir(), "no-such-dir"))
#> [1] FALSE
try(rapl_available(NA_character_))
#> Error : `rapl_dir` must be a single directory path