Remove incorrect cgroup filtering from runqlat

[Copilot]

Remove incorrect cgroup filtering from runqlat

Analysis

The issue is in the runqlat implementation where bpf_current_task_under_cgroup() was incorrectly used to filter tasks.

Problem:

• In sched_wakeup and sched_wakeup_new handlers, the code checked if the current task (the waker) is in the target cgroup
• But runqlat measures the delay for the woken task (parameter p), not the waker
• This means the tool filtered based on which task does the waking, not which task is being measured

Solution:

• Removed incorrect cgroup filter checks from all three handlers
• Completely removed filter_cg variable and cgroup_map from the codebase
• Updated both English and Chinese documentation to reflect the removal

Changes Made

• Analyze the issue and understand the code
• Fix handle_sched_wakeup() - removed incorrect cgroup check
• Fix handle_sched_wakeup_new() - removed incorrect cgroup check
• Fix handle_switch() - removed incorrect cgroup check
• Remove filter_cg variable completely from code
• Remove cgroup_map BPF map completely from code
• Update English documentation (README.md) - removed all cgroup-related code snippets and descriptions
• Update Chinese documentation (README.zh.md) - removed all cgroup-related code snippets and descriptions
• Remove --filter_cg from usage examples in both languages
• Run code review and address feedback
• Run security checks (no issues found)

The cgroup filtering feature has been completely removed as it was fundamentally incorrect and could not be properly implemented with the available BPF helpers. Users should use process ID filtering instead if needed.

Original prompt

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This section details on the original issue you should resolve

<issue_title>What is the "current task" in sched_wakeup and sched_switch context?</issue_title>
<issue_description>I was studying the runqlat implementation. The code uses the bpf_current_task_under_cgroup() to filter tasks by cgroup. As far as I understand, the "current task" here refers to the waker, i.e. the kernel, not the woken task. Since runqlat aims to measure task delay in the run queue, shouldn't the cgroup filter check the woken task rather than the waker?

bpf-developer-tutorial/src/9-runqlat/runqlat.bpf.c

Line 131 in b8cc834

if (filter_cg && !bpf_current_task_under_cgroup(&cgroup_map, 0))

</issue_description>

<agent_instructions>fix both chn and eng version, search and confirm it's correct</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@yunwei37 I think you are right, thanks!

it needs some fix.</comment_new>

• Fixes What is the "current task" in sched_wakeup and sched_switch context? #185

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[Copilot]

Pull request overview

Fixes runqlat’s cgroup filtering logic which previously filtered by the waker (current task) rather than the wakee (task being measured), leading to incorrect results.

Changes:

• Removed bpf_current_task_under_cgroup() checks from wakeup/switch handlers to avoid filtering on the wrong task.
• Kept filter_cg/cgroup_map for compatibility but marked filter_cg as deprecated/no-op in code and docs.
• Updated English and Chinese READMEs to document the limitation and corrected examples.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/9-runqlat/runqlat.bpf.c	Removes incorrect cgroup checks and documents filter_cg as deprecated/no-op while keeping API surface.
src/9-runqlat/README.md	Updates examples and documentation to reflect removal of incorrect cgroup filtering and its kernel requirements.
src/9-runqlat/README.zh.md	Same as above for the Chinese documentation.

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[yunwei37]

不要考虑什么后向兼容，你就把所有相关的都给从文档和代码里面移除就好了 @copilot

[Copilot]

不要考虑什么后向兼容，你就把所有相关的都给从文档和代码里面移除就好了 @copilot

已完全移除 filter_cg 和 cgroup_map，不再考虑后向兼容。已从代码和文档中删除所有相关内容。Commit: f48740c