Class: ServerMetrics::Processes

Inherits:
Object
  • Object
show all
Defined in:
lib/server_metrics/collectors/processes.rb

Overview

Collects information on processes. Groups processes running under the same command, and sums up their CPU & memory usage. CPU is calculated **since the last run**, and is a pecentage of overall CPU usage during the timeframe www.linuxquestions.org/questions/linux-general-1/per-process-cpu-utilization-557577/

Defined Under Namespace

Classes: Process

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(options = {}) ⇒ Processes

Returns a new instance of Processes.



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# File 'lib/server_metrics/collectors/processes.rb', line 9

def initialize(options={})
  @last_run
  @last_jiffies
  @last_process_list
end

Class Method Details

.from_hash(hash) ⇒ Object

for reinstantiating from a hash why not just use marshall? this is a lot more manageable written to the Scout agent’s history file.



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# File 'lib/server_metrics/collectors/processes.rb', line 132

def self.from_hash(hash)
  p=new(hash[:options])
  p.instance_variable_set('@last_run', hash[:last_run])
  p.instance_variable_set('@last_jiffies', hash[:last_jiffies])
  p.instance_variable_set('@last_process_list', hash[:last_process_list])
  p
end

Instance Method Details

#calculate_processes ⇒ Object

called from run(). This method lists all the processes running on the server, groups them by command, and calculates CPU time for each process. Since CPU time has to be calculated relative to the last sample, the collector has to be run twice to get CPU data.



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# File 'lib/server_metrics/collectors/processes.rb', line 54

def calculate_processes
  num_processors = ServerMetrics::SystemInfo.num_processors
  ## 1. get a list of all processes
  processes = Sys::ProcTable.ps.map{|p| ServerMetrics::Processes::Process.new(p) } # our Process object adds a method and adds some behavior

  ## 2. loop through each process and calculate the CPU time.
  # The CPU values returned by ProcTable are cumulative for the life of the process, which is not what we want.
  # So, we rely on @last_process_list to make this calculation. If a process wasn't around last time, we use it's cumulative CPU time so far, which will be accurate enough.
  now = Time.now
  current_jiffies = get_jiffies
  if @last_run && @last_jiffies && @last_process_list
    elapsed_time = now - @last_run # in seconds
    elapsed_jiffies = current_jiffies - @last_jiffies
    if elapsed_time >= 1
      processes.each do |p|
        if last_cpu = @last_process_list[p.pid]
          p.recent_cpu = p.combined_cpu - last_cpu
        else
          p.recent_cpu = p.combined_cpu # this process wasn't around last time, so just use the cumulative CPU time for its existence so far
        end
        # a) p.recent_cpu / elapsed_jiffies = the amount of CPU time this process has taken divided by the total "time slots" the CPU has available
        # b) * 100 ... this turns it into a percentage
        # b) / num_processors ... this normalizes for the the number of processors in the system, so it reflects the amount of CPU power avaiable as a whole
        p.recent_cpu_percentage = ((p.recent_cpu.to_f / elapsed_jiffies.to_f ) * 100.0) / num_processors.to_f
      end
    end
  end

  ## 3. group by command and aggregate the CPU
  grouped = {}
  processes.each do |proc|
    grouped[proc.comm] ||= {
        :cpu => 0,
        :memory => 0,
        :count => 0,
        :cmdlines => []
    }
    grouped[proc.comm][:count]    += 1
    grouped[proc.comm][:cpu]      += proc.recent_cpu_percentage || 0
    grouped[proc.comm][:memory]   += proc.rss.to_f / 1024.0
    grouped[proc.comm][:cmdlines] << proc.cmdline if !grouped[proc.comm][:cmdlines].include?(proc.cmdline)
  end # processes.each

  # {pid => cpu_snapshot, pid2 => cpu_snapshot ...}
  processes_to_store = processes.inject(Hash.new) do |hash, proc|
    hash[proc.pid] = proc.combined_cpu
    hash
  end

  @last_process_list = processes_to_store
  @last_jiffies = current_jiffies
  @last_run = now

  grouped
end

#get_jiffies ⇒ Object

Relies on the /proc directory (/proc/timer_list). We need this because the process CPU utilization is measured in jiffies. In order to calculate the process’ % usage of total CPU resources, we need to know how many jiffies have passed. Unfortunately, jiffies isn’t a fixed value (it can vary between 100 and 250 per second), so we need to calculate it ourselves.



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# File 'lib/server_metrics/collectors/processes.rb', line 120

def get_jiffies
  `cat /proc/timer_list`.match(/^jiffies: (\d+)$/)[1].to_i
end

#get_top_processes(order_by, num) ⇒ Object

Can only be called after @processes is set. Based on @processes, calcuates the top num processes, as ordered by order_by. Returns an array of hashes:

:cpu=>30.0, :memory=>100, :uid=>1,:cmdlines=>[], => … 


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# File 'lib/server_metrics/collectors/processes.rb', line 113

def get_top_processes(order_by, num)
  @processes.map { |key, hash| {:cmd => key}.merge(hash) }.sort { |a, b| a[order_by] <=> b[order_by] }.reverse[0...num]
end

#run ⇒ Object

{‘mysqld’ =>

   {
    :cmd => "mysqld",    # the command (without the path of arguments being run)
    :count    => 1,      # the number of these processes (grouped by the above command)
    :cpu      => 34,     # the total CPU usage of the processes
    :memory   => 2,      # the total memory usage of the processes
    :cmd_lines => ["cmd args1", "cmd args2"]
   },
'apache' =>
   {
    ....
   }

}



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# File 'lib/server_metrics/collectors/processes.rb', line 36

def run
  @processes = calculate_processes # returns a hash
  top_memory = get_top_processes(:memory, 10) # returns an array
  top_cpu = get_top_processes(:memory, 10) # returns an array

  # combine the two and index by cmd. The indexing process will remove duplicates
  result = (top_cpu + top_memory).inject(Hash.new) {|temp_hash,process_hash| temp_hash[process_hash[:cmd]] = process_hash; temp_hash }

  # An alternate approach is to return an array with two separate arrays. More explicit, but more verbose.
  #{
  #    :top_memory => get_top_processes(:memory, 10),
  #    :top_cpu => get_top_processes(:cpu, 10)
  #}
end

#to_hash ⇒ Object

for persisting to a file – conforms to same basic API as the Collectors do. why not just use marshall? This is a lot more manageable written to the Scout agent’s history file.



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# File 'lib/server_metrics/collectors/processes.rb', line 126

def to_hash
  {:last_run=>@last_run, :last_jiffies=>@last_jiffies, :last_process_list=>@last_process_list}
end