Demonstrate the contention on /dev/urandom with N threads.

urandom-reads.py

# Create a user land file for testing.
# dd if=/dev/urandom of=/tmp/urandom bs=1M count=10
#
# urandom-reads.py infile threads
# Examples:
#   time python2.6 urandom-reads.py /tmp/urandom
#   time python2.6 urandom-reads.py /dev/urandom
#
# R to generate a plot of the read time distribution at each level of concurrency
# rdt = read.csv("output.csv", header=F)
# rdt.n = rdt[complete.cases(rdt),]
# ggplot(rdt.n[rdt.n$threads<=16&rdt.n$time<0.1,], aes(x=threads,y=time, fill=as.factor(threads))) +
#   geom_boxplot() + theme(legend.position="none") + scale_x_continuous(breaks=seq(1,16)) +
#   labs(x="Threads", y="Time", title="/dev/urandom 4k Read Distributions")
import multiprocessing, sys, os, time

BYTES=4096
NUM_READS=1000

class UrandomReader(multiprocessing.Process):
    def __init__(self, num_reads, num_bytes, infile, threads):
        self.num_reads = num_reads
        self.num_bytes = num_bytes
        self.infile    = infile
        self.threads   = threads
        multiprocessing.Process.__init__(self)

    def run(self):
        fd = open(self.infile, 'rb')
        for i in range(self.num_reads):
            start = time.time()
            b  = fd.read(self.num_bytes)
            assert(len(b) == self.num_bytes)
            print "%d,%1.4f" % (threads, (time.time() - start))

if __name__ == '__main__':
    if len(sys.argv) < 3:
        print "%s <input-file> <threads>" % sys.argv[0]
        sys.exit(1)

    infile = sys.argv[1]
    threads = int(sys.argv[2])
    assert(threads > 0)
    assert(os.path.exists(infile))

    jobs = []
    for i in range(threads):
        p = UrandomReader(NUM_READS, BYTES, infile, threads)
        jobs.append(p)
        p.start()

    for j in jobs:
        j.join()