Description

tim-one

opened on Mar 21, 2024

Issue body actions

Bug report

Bug description:

That started within the last 48 hours, on the main branch. Here's test code; it's possible it could be simplified

if 1:
    class Obj:
        def __init__(self, i):
            self.val = i

    import sys
    print(sys.version)
    from time import perf_counter as now

    start = now()
    xs = [Obj(i) for i in range(2**21)]
    finish = now()
    print(finish - start)

Under 3.12.2 it takes about a second, but under current main about 21 seconds.

C:\Code\Python\PCbuild>py \MyPy\small.py
3.12.2 (tags/v3.12.2:6abddd9, Feb  6 2024, 21:26:36) [MSC v.1937 64 bit (AMD64)]
0.9562742999987677

C:\Code\Python\PCbuild>amd64\python.exe \MyPy\small.py
3.13.0a5+ (heads/main:f4cc77d494, Mar 20 2024, 20:28:50) [MSC v.1939 64 bit (AMD64)]
20.99507549998816

If the size of the list is increased, it appears to suffer much worse than linear-time slowdown.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• GH-117108: Change the size of the GC increment to about 1% of the total heap size. #117120
• GH-117108: Set the "old space bit" to "visited" for all young objects  #117213

Activity

1. tim-one

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   on Mar 21, 2024
2. hauntsaninja commented on Mar 21, 2024

   

   hauntsaninja

   on Mar 21, 2024

   Contributor

   More actions

   It looks like the regression is due to 1530932 / #116206 cc @markshannon

   Reacted by Tim Peters
3. tim-one commented on Mar 21, 2024

   

   tim-one

   on Mar 21, 2024

   MemberAuthor

   More actions

   Thanks - at least the cause is obvious 😆.,
4. Eclips4

   added

   performancePerformance or resource usagePerformance or resource usage

   on Mar 21, 2024
5. markshannon

   self-assigned this

   on Mar 21, 2024
6. tim-one commented on Mar 21, 2024

   

   tim-one

   on Mar 21, 2024

   MemberAuthor

   More actions

   Noting that, in the original program that triggered this, disabling gc restored its former speed.
7. AlexWaygood

   added

   release-blocker

   and removed

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Mar 21, 2024
8. ezio-melotti

   added this to Release and Deferred blockers 🚫on Mar 21, 2024
9. github-project-automation

   moved this to Todo in Release and Deferred blockers 🚫on Mar 21, 2024
10. AlexWaygood

    added

    type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

    on Mar 22, 2024
11. markshannon

    added a commit that references this issue on Mar 22, 2024

    GH-117108: Change the size of the GC increment to about 1% of the tot…

    e28477f
12. gvanrossum

    added a commit that references this issue on Mar 23, 2024

    Revert "pythonGH-117108: Change the size of the GC increment to about…

    7420a55
13. adorilson

    added a commit that references this issue on Mar 25, 2024

    pythonGH-117108: Change the size of the GC increment to about 1% of t…

    47f5202
14. vstinner

    added a commit that references this issue on Mar 26, 2024

    GH-117108: Set the "old space bit" to "visited" for all young objects (…

    8bef34f
15. pablogsal commented on Mar 26, 2024

    

    pablogsal

    on Mar 26, 2024

    Member

    More actions

    Has this been fixed by either #117120 or #117213?
16. markshannon commented on Mar 26, 2024

    

    markshannon

    on Mar 26, 2024

    Member

    More actions

    It was fixed by #117120

    Reacted by Victor Stinner and bluss
17. tim-one

    closed this as completedon Mar 26, 2024
18. github-project-automation

    moved this from Todo to Done in Release and Deferred blockers 🚫on Mar 26, 2024
19. NGRsoftlab

    added 2 commits that reference this issue on Apr 2, 2024

    Squashed commit of the following:

    1b5fe4c

    Squashed commit of the following:

    a016a54
20. diegorusso

    added 2 commits that reference this issue on Apr 17, 2024

    pythonGH-117108: Change the size of the GC increment to about 1% of t…

    6e59d30

    pythonGH-117108: Set the "old space bit" to "visited" for all young o…

    6ca8a3e
21. Yhg1s

    added 2 commits that reference this issue on Sep 29, 2024

    Revert "pythonGH-117108: Set the "old space bit" to "visited" for all…

    2992289

    Revert "pythonGH-117108: Change the size of the GC increment to about…

    60a248b

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