{-# LANGUAGE TemplateHaskell #-}
-- | Types and operations for the CPU CGroup controller.
module System.CGroup.CPU (
-- * The CPU cgroup controller
CPU,
resolveCPUController,
-- * Operations on the CPU controller
CPUQuota (..),
getCPUQuota,
) where
import Control.Monad ((<=<))
import Path
import System.CGroup.Controller (Controller (..), resolveCGroupController)
-- | The "cpu" cgroup controller
data CPU
-- | Resolve the CPU cgroup controller for the current process
--
-- Throws an Exception if the CPU controller is not able to be found, or when
-- running outside of a cgroup
resolveCPUController :: IO (Controller CPU)
resolveCPUController = resolveCGroupController "cpu"
-- | A CPU quota is the amount of CPU time our process can use relative to the
-- scheduler period
--
-- For example:
--
-- @
-- | cpu.cfs_quota_us | cpu.cfs_period_us | description |
-- | ---------------- | ----------------- | ----------- |
-- | 100000 | 100000 | (1) |
-- | 200000 | 100000 | (2) |
-- | 50000 | 100000 | (3) |
-- | -1 | 100000 | (4) |
-- @
--
-- (1): we can use up to a single CPU core
--
-- (2): we can use up to two CPU cores
--
-- (3): the scheduler will give us a single CPU core for up to 50% of the time
--
-- (4): we can use all available CPU resources (there is no quota)
data CPUQuota
= NoQuota
| -- | cpu.cfs_quota_us, cpu.cfs_period_us
CPUQuota Int Int
deriving (Eq, Ord, Show)
-- | Read a CGroup configuration value from its file
readCGroupInt :: Path b File -> IO Int
readCGroupInt = readIO <=< (readFile . toFilePath)
-- | Get the CPU quota within the given cgroup CPU controller
getCPUQuota :: Controller CPU -> IO CPUQuota
getCPUQuota (Controller root) = do
quota <- readCGroupInt (root </> cpuQuotaPath)
case quota of
(-1) -> pure NoQuota
_ -> CPUQuota quota <$> readCGroupInt (root </> cpuPeriodPath)
-- Path to the "cpu quota" file
--
-- When this file contains "-1", there is no quota set
cpuQuotaPath :: Path Rel File
cpuQuotaPath = $(mkRelFile "cpu.cfs_quota_us")
-- Path to the "cpu period" file
cpuPeriodPath :: Path Rel File
cpuPeriodPath = $(mkRelFile "cpu.cfs_period_us")