René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Dramatic slowdown with random.random on free-threading build.","articleBody":"![out](https://github.com/python/cpython/assets/5110323/753ae6b0-fd71-4b8a-bac4-7f4aa6777a2e)\r\n\r\nThis slowdown was found with one of my favorite benchmarks, which is calculating the pi value with the Monte Carlo method.\r\n\r\n```python\r\nimport os\r\nimport random\r\nimport time\r\nfrom threading import Thread\r\n\r\ndef monte_carlo_pi_part(n: int, idx: int, results: list[int]) -\u003e None:\r\n    count = 0\r\n    for i in range(n):\r\n        x = random.random()\r\n        y = random.random()\r\n\r\n        if x*x + y*y \u003c= 1:\r\n            count += 1\r\n    results[idx] = count\r\n\r\n\r\nn = 10000\r\nthreads = []\r\nnum_threads = 100\r\nresults = [0] * num_threads\r\na = time.time()\r\nfor i in range(num_threads):\r\n    t = Thread(target=monte_carlo_pi_part, args=(n, i, results))\r\n    t.start()\r\n    threads.append(t)\r\n\r\nwhile threads:\r\n    t = threads.pop()\r\n    t.join()\r\n\r\nb = time.time()\r\nprint(sum(results) / (n * num_threads) * 4)\r\nprint(b-a)\r\n```\r\n\r\nAcquiring critical sections for random methods causes this slowdown.\r\nRemoving `@critical_section` from the method, which uses `genrand_uint32` and then updating `genrand_uint32` to use atomic operation makes the performance acceptable.\r\n\r\n| Build                                                  | Elapsed             | PI       |\r\n|--------------------------------------------------------|---------------------|----------|\r\n| Default (with specialization)                          | 0.16528010368347168 | 3.144508 |\r\n| Free-threading (with no specialization)                | 0.548654317855835   | 3.1421   |\r\n| Free-threading with my patch (with no  specialization) | 0.2606849670410156  | 3.141108 |\r\n\r\n\r\n\u003c!-- gh-linked-prs --\u003e\r\n### Linked PRs\r\n* gh-118393\r\n* gh-118396\n\u003c!-- /gh-linked-prs --\u003e\r\n","author":{"url":"https://github.com/corona10","@type":"Person","name":"corona10"},"datePublished":"2024-04-29T14:38:30.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/118392/cpython/issues/118392"}