BlockQuicksort: How Branch Mispredictions don't affect Quicksort · HackerPapers discussions

BlockQuicksort: How Branch Mispredictions don't affect Quicksort — mentioned by Voultapher

Sat, 10 Jun 2023 21:22:27 GMT

Ok so both the things you linked are not my ideas. The first one is AFAIK originally from the BlockQuicksort paper https://arxiv.org/pdf/1604.06697.pdf section 3.2. Which Orson Peters used in his pdqsort, which I know base ipnsort on. The second one is from Igor van den Hoven in his work on quadsort as I mention in the function description. Really a lot of this stuff is building on top of other peoples work and refining it. Seemingly I'm the first to write neat little ASCII graphics for them in the code making them easier to approach. There are some novel ideas by me in there too though, for…

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BlockQuicksort: How Branch Mispredictions don't affect Quicksort — mentioned by sanxiyn

Wed, 10 May 2023 16:44:17 GMT

Theoretical advances are constant (just check the literature), but two particular advances in the last decade are of practical importance: one for sort and one for hash table. As in: check the implementation you are using, if it doesn't incorporate these advances you are leaving substantial performance (2x is not out of the question) on the table. How Branch Mispredictions don't affect Quicksort (2016) https://arxiv.org/abs/1604.06697 Quicksort is still the algorithm of choice for general purpose internal unstable sort. In modern hardwares, quicksort spends a lot of time recovering from…

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BlockQuicksort: How Branch Mispredictions don't affect Quicksort — mentioned by nightcracker

Sun, 18 Jul 2021 16:23:46 GMT

This article is missing the important reference to the prior work by Edelkamp and Weiss, on branchless quicksort [1]. I've long since implemented that in pdqsort [2], along with other techniques described by me in [3] which is a drop-in replacement for std::sort that's ~twice as fast as std::sort for small data with branchless comparisons. It's also available in Boost.sort [4]. [1] https://arxiv.org/abs/1604.06697 [2] https://github.com/orlp/pdqsort [3] https://arxiv.org/abs/2106.05123 [4] https://www.boost.org/doc/libs/1_76_0/libs/sort/doc/html/sor...

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BlockQuicksort: How Branch Mispredictions don't affect Quicksort — mentioned by lorenzhs

Fri, 31 Aug 2018 11:28:11 GMT

Especially when targeting realistic machine models, there are a lot of things that are suboptimal about the classical sorting algorithms like quicksort or mergesort. For example, a quicksort with perfect choice of pivot will incur a branch miss with probability 50% for every element. That's not something classical complexity analysis measures, but on actual CPUs, branch misses have quite an impact (something like 10–15 cycles). Shameless plug for something I once built for a lecture to demonstrate this: https://github.com/lorenzhs/quicksort-pivot-imbalance For sorting algorithms that take the…

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BlockQuicksort: How Branch Mispredictions don't affect Quicksort — mentioned by lorenzhs

Fri, 30 Jun 2017 07:59:15 GMT

To illustrate the point about branch misprediction, I implemented quicksort with intentionally skewed pivot selection. You can see the results here: https://github.com/lorenzhs/quicksort-pivot-imbalance For this demo I'm sorting a permutation of the range 1 to n, so obtaining perfect or arbitrarily skewed pivots is free, which isn't realistic, but that's not the point. My experiments show that quicksort is fastest on my machine when 15% of the elements are on one side and 85% on the other. This is a tradeoff between branch prediction (if it always guesses "right side", it's right 85% of the…

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BlockQuicksort: How Branch Mispredictions don't affect Quicksort — HN submission

Tue, 26 Apr 2016 21:42:26 GMT

BlockQuicksort: How Branch Mispredictions Don't Affect Quicksort

3 points; 0 discussion replies on HN. Paper and source history. A submission is not an endorsement.