88 lines
2.3 KiB
Go
88 lines
2.3 KiB
Go
package main
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import (
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"fmt"
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"io/ioutil"
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"math"
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"path/filepath"
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"strconv"
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"strings"
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)
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const raplPrefixCPU = "intel-rapl"
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// constraint_0 is usually the longer window while constraint_1 is usually the longer window
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const maxPowerFileShortWindow = "constraint_0_max_power_uw"
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const powerLimitFileShortWindow = "constraint_0_power_limit_uw"
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// capNode uses pseudo files made available by the Linux kernel
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// in order to capNode CPU power. More information is available at:
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// https://www.kernel.org/doc/html/latest/power/powercap/powercap.html
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func capNode(base string, percentage int) error {
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if percentage <= 0 || percentage > 100 {
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return fmt.Errorf("cap percentage must be between 0 (non-inclusive) and 100 (inclusive): %d", percentage)
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}
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files, err := ioutil.ReadDir(base)
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if err != nil {
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return err
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}
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for _, file := range files {
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fields := strings.Split(file.Name(), ":")
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// Fields should be in the form intel-rapl:X where X is the power zone
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// We ignore sub-zones which follow the form intel-rapl:X:Y
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if len(fields) != 2 {
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continue
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}
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if fields[0] == raplPrefixCPU {
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maxPower, err := maxPower(filepath.Join(base, file.Name(), maxPowerFileShortWindow))
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if err != nil {
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fmt.Println("unable to retreive max power for zone ", err)
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continue
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}
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// We use floats to mitigate the possibility of an integer overflows.
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powercap := uint64(math.Ceil(float64(maxPower) * (float64(percentage) / 100)))
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err = capZone(filepath.Join(base, file.Name(), powerLimitFileShortWindow), powercap)
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if err != nil {
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fmt.Println("unable to write powercap value: ", err)
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continue
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}
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fmt.Println(file.Name(), ": ", int(maxPower), ", ", int(powercap))
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}
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}
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return nil
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}
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// maxPower returns the value in float of the maximum watts a power zone
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// can use.
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func maxPower(zone string) (uint64, error) {
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maxPower, err := ioutil.ReadFile(zone)
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if err != nil {
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return 0.0, err
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}
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maxPoweruW, err := strconv.ParseUint(strings.TrimSpace(string(maxPower)), 10, 64)
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if err != nil {
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return 0.0, err
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}
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return maxPoweruW, nil
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}
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// capZone caps a power zone to a specific amount of watts specified by value
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func capZone(zone string, value uint64) error {
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err := ioutil.WriteFile(zone, []byte(strconv.FormatUint(value, 10)), 0644)
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if err != nil {
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return err
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}
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return nil
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}
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