Question

I work on shared linux machines with between 4 and 24 cores. To make best use of them, I use the following code to detect the number of processors from my ruby scripts:

return `cat /proc/cpuinfo | grep processor | wc -l`.to_i

(perhaps there is a pure-ruby way of doing this?)

But sometimes a colleague is using six or eight of the 24 cores. (as seen via top). How can I get an estimate of the number of currently unused processors that I can use without making anyone upset?

Thanks!

Answer 1

You can use the data in the /proc filesystem to get CPU affinity info for running processes. The following should give you the number of CPUs currently in use (Note: I don’t have a Linux or Ruby box handy so this code is untested, but you can get the idea):

def processors_in_use
    procs=[]
    Dir.glob("/proc/*/stat") {|filename|
        next if File.directory?(filename)
        this_proc=[]
        File.open(filename) {|file| this_proc = file.gets.split.values_at(2,38)}
        procs << this_proc[1].to_i if this_proc[0]=="R"
    }
    procs.uniq.length
end

def num_processors
    IO.readlines("/proc/cpuinfo").delete_if{|x| x.index("processor")==nil}.length
end

def num_free_processors
    num_processors - processors_in_use
end

def estimate_free_cpus(count, waittime)
    results=[]
    count.times {
        results << num_free_processors
        sleep(waittime)
    }
    sum=0
    results.each {|x| sum += x}
    (sum.to_f / results.length).round
end

Edit: I verified that the above code works (I was using Ruby 1.9)