vfscount(8)

📦 version 0.36.1, in centos-stream 10, centos-stream 9, fedora 43, fedora 44

✨ vfscount(8) — System Manager's Manual ✨

💖 NAME 💖

vfscount — okay so this one counts VFS calls (anything matching "vfs_*") 🧮 It uses Linux eBPF/bcc, so it's lowkey a whole vibe. ✨

🎀 SYNOPSIS 🎀

vfscount [duration]

🦋 DESCRIPTION 🦋

Okay so this tool counts VFS calls 📊 It's super useful for general workload characterization of these operations, aka figuring out what your system is actually doing all day 🫶

Here's the tea: it works by tracing all kernel functions beginning with "vfs_" using dynamic tracing. ⚠️ That might match more functions than you actually care about, so if you want to measure something specific, edit the script to customize which functions get traced 💅

Also, since this uses BPF, only the root user can use this tool 👑 no sneaking in as a regular user, bestie 🙈

🌸 REQUIREMENTS 🌸

You need CONFIG_BPF and bcc 🔧 no cap, you can't skip these ones 😭

🍓 OPTIONS 🍓

  • duration — how long the trace runs, in seconds ⏱️

🧚 EXAMPLES 🧚

Count some VFS calls until you hit Ctrl-C 🛑 (the classic move):

# vfscount

Count some VFS calls for ten seconds exactly ⏰:

# vfscount 10

💜 FIELDS 💜

  • ADDR — the address of the instruction pointer that got traced 🔍 This is only really useful if the FUNC column looks sus and you want to double check the translation 🕵️‍♀️
  • FUNC — the kernel function name 🧠
  • COUNT — how many times it got called while tracing 🔢

🌈 OVERHEAD 🌈

This one is actually pretty efficient, bestie ✨ It traces kernel vfs functions and keeps the counts in-kernel, which then get asynchronously copied over to user-space 🚀 Even though VFS operations can be super high-rate (>1M/sec), this is a relatively efficient way to trace these events, so the overhead is expected to be small for normal workloads 💪

⚠️ Measure in a test environment first! If overhead is an issue, edit the script to reduce the types of vfs functions traced (currently all beginning with "vfs_"). Don't say I didn't warn you 😭

🫶 SOURCE 🫶

This comes from bcc 🐝

https://github.com/iovisor/bcc

Also, look in the bcc distribution for a companion _examples.txt file with example usage, output, and commentary for this tool 📚 it's giving helpful.

🔥 OS 🔥

Linux 🐧

🙈 STABILITY 🙈

Unstable — it's still in development, so don't be shocked if things shift 🚧

👑 AUTHOR 👑

Brendan Gregg 💅

⭐ SEE ALSO ⭐

vfsstat(8) — go check it out, it's the iconic sibling 🦋

Filed under USER COMMANDS, last updated 2015-08-18, and it's still vfscount(8) forever 💖 Stay curious, bestie ✨🎀

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