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Posts tagged with 'rdrand'

Colin Ian King

Intel rdrand instruction revisited

A few months ago I did a quick and dirty benchmark of the Intel rdrand instruction found on the new Ivybridge processors.  I did some further analysis a while ago and I've only just got around to writing up my findings. I've improved the test by exercising the Intel Digital Random Number Generator (DRNG) with multiple threads and also re-writing the rdrand wrapper in assembler and ensuring the code is inline'd.  The source code for this test is available here.

So, how does it shape up?  On a i5-3210M (2.5GHz) Ivybridge (2 cores, 4 threads) I get a peak of ~99.6 million 64 bit rdrands per second with 4 threads which equates to ~6.374 billion bits per second.  Not bad at all.

With a 4 threaded i5-3210M CPU we hit maximum rdrand throughput with 4 threads.

..and with a 8 threaded i7-3770 (3.4GHz) Ivybridge (4 cores, 8 threads) we again hit a peak throughput of 99.6 million 64 bit rdrands a second on 3 threads. One can therefore conclude that this is the peak rate of the DNRG on both CPUs tested.  A 2 threaded i3 Ivybridge CPU won't be able to hit the peak rate of the DNRG, and a 4 threaded i5 can only just max out the DNRG with some hand-optimized code.

Now how random is this random data?  There are several tests available; I chose to exercise the DRNG using the dieharder test suite.  The test is relatively simple; install dieharder and do 64 bit rdrand reads and output these as a raw random number stream and pipe this into dieharder:

 sudo apt-get install dieharder  
./rdrand-test | dieharder -g 200 -a
# dieharder version 3.31.1 Copyright 2003 Robert G. Brown #
rng_name |rands/second| Seed |
stdin_input_raw| 3.66e+07 | 639263374|
test_name |ntup| tsamples |psamples| p-value |Assessment
diehard_birthdays| 0| 100| 100|0.40629140| PASSED
diehard_operm5| 0| 1000000| 100|0.79942347| PASSED
diehard_rank_32x32| 0| 40000| 100|0.35142889| PASSED
diehard_rank_6x8| 0| 100000| 100|0.75739694| PASSED
diehard_bitstream| 0| 2097152| 100|0.65986567| PASSED
diehard_opso| 0| 2097152| 100|0.24791918| PASSED
diehard_oqso| 0| 2097152| 100|0.36850828| PASSED
diehard_dna| 0| 2097152| 100|0.52727856| PASSED
diehard_count_1s_str| 0| 256000| 100|0.08299753| PASSED
diehard_count_1s_byt| 0| 256000| 100|0.31139908| PASSED
diehard_parking_lot| 0| 12000| 100|0.47786440| PASSED
diehard_2dsphere| 2| 8000| 100|0.93639860| PASSED
diehard_3dsphere| 3| 4000| 100|0.43241488| PASSED
diehard_squeeze| 0| 100000| 100|0.99088862| PASSED
diehard_sums| 0| 100| 100|0.00422846| WEAK
diehard_runs| 0| 100000| 100|0.48432365| PASSED
dab_monobit2| 12| 65000000| 1|0.98439048| PASSED

..and leave to cook for about 45 minutes.  The -g 200 option specifies that the random numbers come from stdin and the -a option runs all the dieharder tests.  All the tests passed with the exception of the diehard_sums test which produced "weak" results, however, this test is known to be unreliable and recommended not to be used.  Quite honestly, I would be surprised if the tests failed, but you never know until one runs them.

The CA cert research labs have an on-line random number generator analysis website allowing one to submit and test at least 12 MB of random numbers. I submitted 32 MB of data, and I am currently waiting to see if I get any results back.  Watch this space.

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Colin Ian King

Simple performance test of rdrand

My new Lenovo X230 laptop is equipped with a Intel(R) i5-3210M CPU (2.5 GHz, with 3.1 GHz Turbo) which supports the new Digital Random Number Generator (DRNG) - a high performance entropy and random number generator.  The DNRG is read using the new Intel rdrand instruction which can return 64, 32 or 16 bit random numbers.

The DRNG is described in detail in this article and provides very useful code examples in assembler and C which I used to write a simple and naive test to see how well the rdrand performs on my i5-3210M.

For my test, I simply read 100 million 64 bit random numbers on a single thread. The Intel literature states one can get up to about 70 million rdrand invocations per second on 8 threads, so my simple test is rather naive as it only exercises rdrand on one thread.  For a set of 10 iterations on my test, I'm getting around 40-45 nanoseconds per rdrand, or about 22-25 million rdrands per second, which is really impressive.   The test is a mix of assembler and C, and is not totally optimal, so I am sure I can squeeze a little more performance out with some extra work.

The next test I suspect is to see just random the data is and to see how well it compares to other software random number generators... but I will tinker with that after my vacation.

Anyhow, for reference, the test can be found here in my git repository.

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