Adjusting default scheduler

The default scheduler (rules/scheduler.lua) uses a decision tree. You can have different configurations that are set in the ulatencyd.conf, but only one can be active at any time.

The scheduler finds it's decision by traveling down the rules top to bottom and checking each entry. The first rule that matches will be used. If the rule contains children rules, these are checked in the same manner.

Lets look at the default config:

SCHEDULER_MAPPING_DESKTOP["cm"] =
{
  {
    name = "system_essential",
    cgroups_name = "sys_essential",
    param = { ["cpu.shares"]="3048" },
    label = { "system.essential" }
  },
  {
    name = "user",
    cgroups_name = "usr_${euid}",
    check = function(proc)
              return ( proc.euid > 999 )
            end,
    param = { ["cpu.shares"]="3048" },
    children = {
      { 
        ...

cm is the cgroups toplevel tree configured in cgroups.conf. If no cgroups subsystem is available from this group, the tree is skipped. The scheduler will start looking at system_essential if it matches, it will use it, if not, user is checked and so on.

Entries of a map

Lets look at at one entry:

{
  name = "sometest",
  cgroups_name = "test_${euid}",
  label = { "testflag" }
  check = function(proc)
            return ( proc.euid == 1020 )
          end,
  param = { ["cpu.shares"]="1001" },
}

• name is a human readable entry, not necessary but good to have.
• cgroups_name is the name to use for creating the subdirectory in cgroups. If it is a string, values written with ${NAME} will be substituted by the values of the process object. If it is a function, it gets the process as first argument and must return a string.
• label is a table of strings that are checked against the flags of the process. If any flags name matches any entry of the label list, the rule matches. If label and a check function exists, the check function is only called when the label matches.
• check(proc) is a function that will be called with the process. If it returns true, the rule matches.
• param are the default parameters that will be used for this cgroup. They represent the cgroups subsystem values set for the subsystems mounted. cm for example mounts the cpu, cpuset and memory subsystem. Names starting with "?" will be silently ignored on writing errors. cpu.shares represent the amount of of cpu power this group will get. For values see the cgroups documentation below.
• adjust(cgroup, proc) is a function that is called with the cgroup and proc object. It can adjust the cgroup parameter for better fitting. Important: this function is called everytime a process runs through.
• adjust_new(cgroup, proc) this function is only called once a new cgroup is created. When a cgroup does not have any processes anymore, it is deleted and the adjust_new function will be called again.

If this does not fit

If the default mapping does not suite you, write another. It would be great if you share it by adding it as a ticket.

If this rule based approach does not fit you, you can replace it with something different by editing rules/scheduler.lua

cgroups documentation

• cpu scheduler
• cgroups docs
• blockio docs