[Haskell-cafe] Splittable random numbers

Ryan Newton newton at mit.edu
Tue Feb 1 06:51:38 CET 2011

Small update:

I got the first results from the hardware accelerated version on a 3.33 ghz
westmere machine.  Right now it does twice as well as the Gladman software
version, which is also twice as well as the System.Random stdgen, and 1000
times faster than a the Haskell implementation of AES that I got from the
Crypto package:

     How many random numbers can we generate in a second on one thread?
      Cost of rdtsc (ffi call):    84
      Approx getCPUTime calls per second: 209,798
      Approx clock frequency:  3,331,093,772
      First, timing with System.Random interface:
 76,811,104 random ints generated [constant zero gen]
 14,482,725 random ints generated [System.Random stdGen]
     16,061 random ints generated [PureHaskell/reference]
     32,309 random ints generated [PureHaskell]
  2,401,893 random ints generated [Gladman inefficient]
 15,980,625 random ints generated [Gladman]
  2,329,500 random ints generated [IntelAES inefficient]
 32,383,799 random ints generated [IntelAES]
      Comparison to C's rand():
 71,392,408 random ints generated [rand/store in C loop]
 71,347,778 random ints generated [rand in Haskell loop]
 71,324,158 random ints generated [rand/store in Haskell loop]

This is what Burton Smith originally thought, that AES based RNG would be
pretty fast and even faster with hardware acceleration.


On Mon, Jan 31, 2011 at 1:25 AM, Ryan Newton <newton at mit.edu> wrote:

> Hi Cafe,
> I've included Gladman's efficient, portable C implementation of AES
> generating random numbers now, and the hardware-accelerated version is
> working too.  I'm currently seeing higher throughput for even the software
> based version than the builtin stdGen:
>   First, timing with System.Random interface:
>      13,051,964 random ints generated [System.Random stdGen]      ~ 252
> cycles/int
>          15,635 random ints generated [PureHaskell/reference]     ~ 210,763
> cycles/int
>          31,159 random ints generated [PureHaskell]               ~ 105,757
> cycles/int
>       2,180,488 random ints generated [Gladman inefficient]       ~ 1,511
> cycles/int
>      15,015,095 random ints generated [Gladman]                   ~ 219
> cycles/int
> That seems like a good argument for cryptographic RNGs to me!
> I'm having a lot of trouble getting cabal to build/install it
> successfully.  You can see what I've got there now.  I'd be interested to
> know if anyone else can build it successfully.  It should work -- but only
> by building the assembly code into a .so and assuming the build directory is
> /opt/intel-aes ;-).
> I don't have real numbers for the hardware version yet because the Westmere
> machine I'm logged into is redhat 5.4 and is giving me "GLIBC_2.7 not found"
> errors.  You can run it for correctness purposes using an emulation tool
> called sde (software development emulator)<http://software.intel.com/en-us/articles/intel-software-development-emulator/>that's based on dynamic binary translation.
> -Ryan
> P.S. Checkout command:
> git clone git://github.com/rrnewton/intel-aes.git
> On Sat, Jan 29, 2011 at 8:52 AM, Ryan Newton <rrnewton at gmail.com> wrote:
>>  perhaps performance? Is this approach less robust with a faster,
>>> non-cryptographic RNG?
>> Yes, I don't understand that either.  Is there a reason that using a
>> weaker PRNG in this case is WORSE than using it in the non-splitting case?
>> Is that why there is more of an impetus to use the cryptographic approach in
>> this case?
>> Anyway, taking for granted that the Burton approach is a useful thing to
>> have implemented, I started developing a package for this stuff -- AES based
>> RNG including both a haskell implementation and wrapping an AESNI-based C
>> one .  I haven't posted it to Hackage yet, but you can find the git
>> repository here:
>>     https://github.com/rrnewton/intel-aes
>> If you build with cabal and run the benchmark-intel-aes-rng executable, it
>> will give you a breakdown like this:
>>     How many random numbers can we generate in a second on one thread?
>>       Cost of rdtsc (ffi call):    83
>>       Approx getCPUTime calls per second: 205,640
>>       Approx clock frequency:  3,306,891,339
>>       First, timing with System.Random interface:
>>        193,178,901 random ints generated [constant zero gen]
>>         14,530,358 random ints generated [System.Random stdGen]
>>             16,346 random ints generated [BurtonGenSlow/reference]
>>             32,965 random ints generated [BurtonGenSlow]
>>       Comparison to C's rand():
>>        118,766,285 random ints generated [rand/store in C loop]
>>        114,668,028 random ints generated [rand / Haskell loop]
>>        114,675,116 random ints generated [rand/store Haskell]
>> At the moment this is Haskell-only, I haven't included the wrapped Intel
>> assembly code library yet.  As you can see, the pure-Haskell AES based RNG
>> (BurtonGenSlow) is pretty slow.
>> Would anyone else be interested in running those RNG testing tools
>> (diehard, big crush) on this to make sure it is working correctly?
>> Also I'd be happy if anyone with a performance-oriented-eye would like to
>> take a look at what's going on.  Both for the sake of the serial performance
>> (above) and because the parallel performance is currently *mysterious*(see below).
>> I figure one of the main reasons for splittable RNG is deterministic
>> parallel computations.  Thus it's important that all threads be able to run
>> the RNG efficiently.  Right now, if you look at SimpleRNGBench.hs I'm just
>> running the same RNG on numCapabilities threads.  Yet with that simple test
>> I'm running into problems, summarized thus:
>>   * I get substantial (3X) variance in program performance on consecutive
>> runs.
>>   * I see a minor hit in performance adding -threaded, but going from -N1
>> to -N4 (even with a single-thread of work) yields a big hit in performance
>> and increase in variance.
>>   * -N4 with four actual threads of work is actually pretty good for the
>> pure haskell version.  All four threads on my nehalem 3.33ghz can maintain
>> 93% of their throughput in the serial case.  BUT the variance problem
>> persists.
>>   * I run a busy-wait loop that measures cpu frequency... and this seems
>> to get messed up in threaded mode (even with -qm -qa).  I don't know why.
>>   * I cannot killThread a haskell thread (forkIO or forkOS) that is
>> currently running a divergent FFI call (safe or unsafe).  (See "time_c".)
>> You can find the details in the DEVLOG here:
>>    https://github.com/rrnewton/intel-aes/blob/master/CHANGELOG
>> Let me know if you have any ideas.  I'm going to leave the Haskell version
>> how it is and focus on wrapping the Intel asm (which has a permissive
>> license).
>> Cheers,
>>   -Ryan
>> P.S. Regarding this benchmarking -- would it be appropriate to use
>> Criterion for this?  Or is it sufficient to measure aggregate throughput as
>> I've been doing?
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