Re: [Haskell-cafe] proper way to generate a random data in criterion

On 19 October 2011 19:21, Gregory Collins wrote:

On Wed, Oct 19, 2011 at 10:13 AM, Kazu Yamamoto wrote:

...

Hello,

I'm measuring performance of the insertion operation of red-black trees. For input, three kinds of [Int] are prepared: the increasing the order, decreasing order, and random.

The random case is 4 or 5 times slower than the others. I'm afraid that my program also measured the cost of random Int generation.

My benchmark code can be found:

       https://github.com/kazu-yamamoto/llrbtree/blob/master/bench/insert/Bench.hs

Does anyone kindly take a look and tell me whether or not my criterion code measures the cost of random Int generation? If so, would you suggest how to avoid it?

The code looks ok to me -- you've deepseq'ed the list, and forcing it to whnf should force the deepseq. Also, criterion runs your benchmark many times, if your code was measuring the RNG time it would only happen once. This would show up in the criterion output as an unusually large outlier.

Wouldn't it be better to write a sensible NFData instance than to explicitly use deepseq? However, you could try to fix this by using an actual seed rather than mkStdGen; this would _really_ give you random values to let you see whether different runtimes affect matters.

G -- Gregory Collins

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