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lib/osutil: Don't attempt to reduce our niceness level (fixes #4681)

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GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4682
This commit is contained in:
Jakob Borg 2018-01-18 08:34:56 +00:00
parent 91210cbb49
commit c2119c9e62
2 changed files with 45 additions and 6 deletions
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39
lib/osutil/lowprio_linux.go
View File

@ -42,23 +42,52 @@ func ioprioSet(class ioprioClass, value int) error {
// SetLowPriority lowers the process CPU scheduling priority, and possibly
// I/O priority depending on the platform and OS.
func SetLowPriority() error {
// Process zero is "self", niceness value 9 is something between 0
// (default) and 19 (worst priority). But then, this is Linux, so of
// course we get this to take care of as well:
//
// "C library/kernel differences
//
// Within the kernel, nice values are actually represented using the
// range 40..1 (since negative numbers are error codes) and these are
// the values employed by the setpriority() and getpriority() system
// calls. The glibc wrapper functions for these system calls handle the
// translations between the user-land and kernel representations of the
// nice value according to the formula unice = 20 - knice. (Thus, the
// kernel's 40..1 range corresponds to the range -20..19 as seen by user
// space.)"
const (
pidSelf = 0
wantNiceLevel = 20 - 9
)
// Remember Linux kernel nice levels are upside down.
if cur, err := syscall.Getpriority(syscall.PRIO_PROCESS, 0); err == nil && cur <= wantNiceLevel {
// We're done here.
return nil
}
// Move ourselves to a new process group so that we can use the process
// group variants of Setpriority etc to affect all of our threads in one
// go. If this fails, bail, so that we don't affect things we shouldn't.
// If we are already the leader of our own process group, do nothing.
if pgid, err := syscall.Getpgid(0); err != nil {
//
// Oh and this is because Linux doesn't follow the POSIX threading model
// where setting the niceness of the process would actually set the
// niceness of the process, instead it just affects the current thread
// so we need this workaround...
if pgid, err := syscall.Getpgid(pidSelf); err != nil {
// This error really shouldn't happen
return errors.Wrap(err, "get process group")
} else if pgid != os.Getpid() {
// We are not process group leader. Elevate!
if err := syscall.Setpgid(0, 0); err != nil {
if err := syscall.Setpgid(pidSelf, 0); err != nil {
return errors.Wrap(err, "set process group")
}
}
// Process zero is "self", niceness value 9 is something between 0
// (default) and 19 (worst priority).
if err := syscall.Setpriority(syscall.PRIO_PGRP, 0, 9); err != nil {
if err := syscall.Setpriority(syscall.PRIO_PGRP, pidSelf, wantNiceLevel); err != nil {
return errors.Wrap(err, "set niceness")
}

12
lib/osutil/lowprio_unix.go
View File

@ -19,6 +19,16 @@ import (
func SetLowPriority() error {
// Process zero is "self", niceness value 9 is something between 0
// (default) and 19 (worst priority).
err := syscall.Setpriority(syscall.PRIO_PROCESS, 0, 9)
const (
pidSelf = 0
wantNiceLevel = 9
)
if cur, err := syscall.Getpriority(syscall.PRIO_PROCESS, pidSelf); err == nil && cur >= wantNiceLevel {
// We're done here.
return nil
}
err := syscall.Setpriority(syscall.PRIO_PROCESS, pidSelf, wantNiceLevel)
return errors.Wrap(err, "set niceness") // wraps nil as nil
}