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Add and remove CPU from epoch computation on active and idle #3920

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Add and remove CPU from epoch computation on active and idle #3920

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Alan-Jowett
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@Alan-Jowett Alan-Jowett commented Oct 8, 2024 •
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Description

Restore the changes reverted by 205802b and fix a bug that was causing use after free (the for loop for computing oldest epoch was malformed resulting in a no-op).

Note: This is intentionally three or more commits:

  1. Restore the reverted code (including the bug).
  2. Fix the bug.
  3. PR feedback and addition of new tests.

Testing

CI/CD + 24 hour run of api_test.exe (previously failing after 2 hours).

Documentation

Yes, in the files.

Installation

No.

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@CodiumAI-Agent /review

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CodiumAI-Agent commented Oct 8, 2024 •
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PR Reviewer Guide 🔍

(Review updated until commit af048fb)

Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 4 🔵🔵🔵🔵⚪
🧪 PR contains tests
🔒 No security concerns identified
⚡ Recommended focus areas for review

Thread Safety
The code modifies shared state without sufficient synchronization mechanisms in several places, which could lead to race conditions or data corruption in a multi-threaded environment.

Resource Leak
The new implementation introduces potential resource leaks where allocated resources on error paths are not always properly freed or handled.

Error Handling
Error paths may not correctly restore previous states, potentially leaving the system in an inconsistent state after an error.

dthaler
dthaler reviewed Oct 8, 2024
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libs/runtime/ebpf_epoch.c Outdated Show resolved Hide resolved
dthaler
dthaler reviewed Oct 8, 2024
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@Alan-Jowett Alan-Jowett force-pushed the cpu_activation branch 6 times, most recently from 7b60ca4 to 6dfd02b Compare October 9, 2024 18:24
hawkinsw
hawkinsw reviewed Oct 10, 2024
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I hope that what I wrote isn't too annoying.

libs/runtime/unit/platform_unit_test.cpp Outdated Show resolved Hide resolved
@Alan-Jowett Alan-Jowett marked this pull request as ready for review October 10, 2024 04:11
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I hope that what I wrote isn't too annoying.

No, I loved it. I dislike that en-gb and en-us differ like this :-P

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Persistent review updated to latest commit af048fb

dthaler
dthaler reviewed Oct 10, 2024
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libs/runtime/ebpf_epoch.c Outdated Show resolved Hide resolved
@Alan-Jowett Alan-Jowett force-pushed the cpu_activation branch 2 times, most recently from 1b357e6 to 0bb37d0 Compare October 10, 2024 18:53
@Alan-Jowett Alan-Jowett marked this pull request as draft October 16, 2024 22:14
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Converting to draft until usersim bug is fixed.

@Alan-Jowett Alan-Jowett force-pushed the cpu_activation branch 2 times, most recently from 88d6e89 to 98263a7 Compare November 3, 2024 23:00
@Alan-Jowett Alan-Jowett force-pushed the cpu_activation branch 2 times, most recently from d4a4a2b to 9ed7807 Compare November 21, 2024 23:39
@Alan-Jowett Alan-Jowett marked this pull request as ready for review November 21, 2024 23:39
mikeagun
mikeagun reviewed Dec 2, 2024
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libs/runtime/ebpf_epoch.c

while (entry != &cpu_entry->epoch_state_list) {
// Walk over each thread_entry in the epoch_state_list and compute the minimum epoch.
for (ebpf_list_entry_t* entry = cpu_entry->epoch_state_list.Flink; entry != &cpu_entry->epoch_state_list;
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If we were activating, do we still need to iterate over the state list? Won't the current epoch of everything on this CPU still be EBPF_EPOCH_UNKNOWN (even though we've updated the freed epoch).

Also, should the current epoch (as well as freed_epoch) for each state entry be updated to current_epoch in the above loop?

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Actually, I think it would be current_epoch-1 for the start epoch of the threads that started while we were activating, since this is the first propose since we started activation.

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Alan-Jowett commented Dec 3, 2024 •
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Switching to draft until usersim is fixed microsoft/usersim#224

@Alan-Jowett Alan-Jowett marked this pull request as draft December 3, 2024 17:16
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@Alan-Jowett @CodiumAI-Agent @mikeagun @dthaler @hawkinsw