dcstat(8)

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

🎀 dcstat(8) 🎀

dcstat - Directory entry cache (dcache) stats. Uses Linux eBPF/bcc. ✨

🌸 SYNOPSIS 🌸

dcstat [interval [count]]

💖 DESCRIPTION 💖

okay so the Linux directory entry cache (dcache) is what makes file and directory name lookups feel fast 🏎️💨 it's giving performance, no cap. this tool spits out per-second summary stats of how the dcache is doing 📊✨

this uses kernel dynamic tracing on the kernel functions lookup_fast() and d_lookup() 🔍 and fair warning, those will probably need updating whenever the kernel changes 🙈 so keep that in mind bestie

⚠️ since this uses BPF, only the root user can run this tool. sorry, not sorry 💅

🧚 REQUIREMENTS 🧚

CONFIG_BPF and bcc. 🔧

🍓 EXAMPLES 🍓

Print summaries each second:

# dcstat

Print output every five seconds, three times:

# dcstat 5 3

📊 FIELDS 📊

  • REFS/s — number of dcache lookups (references) per second. the main character count 👑
  • SLOW/s — number of dcache lookups that failed the lookup_fast() path and had to run the lookup_slow() path instead 🐢
  • MISS/s — number of dcache misses, meaning lookups that failed both the fast and slow paths 💀
  • HIT% — percentage of dcache hits out of the total references 💯

🦋 OVERHEAD 🦋

the overhead depends on how often file and directory name lookups happen 🫠 the per-event overhead is low, lowkey, but some apps can do over 100k lookups per second 😭 at that point the low per-event cost starts adding up and could become measurable (over 10% CPU usage) 🔥

🧪 measure this in a test environment first, please and thank you.

🌈 SOURCE 🌈

this is from bcc 💜

https://github.com/iovisor/bcc

also check out the companion _examples.txt file in the bcc distribution. it has example usage, output, and commentary for this tool 📝

🐧 OS 🐧

Linux 🐧

🙈 STABILITY 🙈

Unstable - in development. it's still cooking, so be gentle 🍳

👩‍💻 AUTHOR 👩‍💻

Brendan Gregg, the legend himself 👑🫶

🔗 SEE ALSO 🔗

  • dcsnoop(8) — the sibling tool you should check out next 🦋

Manual page dcstat(8) from USER COMMANDS, dated 2016-02-09, signing off with love 💖✨ bye bestie 🎀💅

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