Add startup latency measurement script

[geertj]

This script measures the startup latency of gcsfuse by launching it in a subprocess, polling the mount point until its device ID (st_dev) changes, and recording the elapsed time.

Examples of running the script:

1. With HNS enabled (default): $ python3 perfmetrics/scripts/startup_latency/startup_latency.py \ --bucket-name geertj-us-central1-a --mount-point ./mnt Startup latency: 360.27 ms

2. With HNS disabled: $ python3 perfmetrics/scripts/startup_latency/startup_latency.py \ --bucket-name geertj-us-central1-a --mount-point ./mnt \ --flags="--enable-hns=false" Startup latency: 28.55 ms

TAG=agy
CONV=cebcc159-cc87-4c47-b800-09dc13fad1ec

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a diagnostic utility designed to quantify the startup performance of gcsfuse. By automating the mounting process and tracking the time taken for the mount point to become active, it provides a reliable way to benchmark startup times under various configurations.

Highlights

• New Performance Tool: Added a Python script to measure the startup latency of gcsfuse by monitoring device ID changes at the mount point.
• Process Management: The script handles gcsfuse process lifecycle, including forced foreground execution, cleanup via unmounting, and timeout management.

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[github-actions]

Hey there and thank you for opening this pull request! 👋🏼

We require pull request titles to follow the Conventional Commits specification and it looks like your proposed title needs to be adjusted.

Details:

No release type found in pull request title "Add startup latency measurement script". Add a prefix to indicate what kind of release this pull request corresponds to. For reference, see https://www.conventionalcommits.org/

Available types:
 - feat: A new feature
 - fix: A bug fix
 - docs: Documentation only changes
 - style: Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc)
 - refactor: A code change that neither fixes a bug nor adds a feature
 - perf: A code change that improves performance
 - test: Adding missing tests or correcting existing tests
 - build: Changes that affect the build system or external dependencies (example scopes: gulp, broccoli, npm)
 - ci: Changes to our CI configuration files and scripts (example scopes: Travis, Circle, BrowserStack, SauceLabs)
 - chore: Other changes that don't modify src or test files
 - revert: Reverts a previous commit

[gemini-code-assist]

Code Review

This pull request introduces a new Python script, startup_latency.py, designed to measure the startup latency of gcsfuse by monitoring the mount point's device ID. The review feedback highlights critical issues in the process management of measure_startup_latency, including potential deadlocks from calling process.wait() unconditionally, a potential NameError if subprocess.Popen fails, and a potential FileNotFoundError if fusermount is missing. A robust refactoring is suggested to safely handle process execution, timeouts, and cleanup.

[charith87]

Standalone script. Seems fine.