llcstat(8)

💖 llcstat(8) ✨ NAME ✨

okay so llcstat is the tool that summarizes CPU cache references and cache misses by process 🧚. it's Linux eBPF/bcc based, so it's giving low-level and iconic 💅

🎀 SYNOPSIS 🎀

llcstat [-h] [-c SAMPLE_PERIOD] [duration]

🌸 DESCRIPTION 🌸

bestie, so llcstat instruments CPU cache references and cache misses on the system side 👀 and summarizes them by PID and CPU. these events mean different things on different architectures. on x86-64, they mean misses and references to LLC 🦋. this is lowkey super useful for finding and debugging performance issues caused by a bad cache hit rate 😭🔥

here's how it works: it samples the matching events defined in uapi/linux/perf_event.h, namely PERF_COUNT_HW_CACHE_REFERENCES and PERF_COUNT_HW_CACHE_MISSES, using BPF perf event tracing ✨. every time an event gets sampled, the attached BPF program records the PID and the CPU ID where it happened, then stores it in table. main character energy 👑

this makes use of a Linux 4.9 feature (BPF_PROG_TYPE_PERF_EVENT) 🌈

⚠️ since this uses BPF, only the root user can use this tool 🙈 no cap, sudo or bust.

🧚 REQUIREMENTS 🧚

you'll need CONFIG_BPF and bcc 💜

✨ OPTIONS ✨

• -h — pulls up the usage message 📖
• -c SAMPLE_PERIOD — samples one in this many cache reference and cache miss events 🎯
• -t — summarizes cache references and misses by PID/TID 💅
• duration — how long to trace, in seconds ⏱️

🍓 EXAMPLES 🍓

bestie wants 1 in 100 events, traced for 20 seconds? it's giving:

# llcstat -c 100 20

🦋 FIELDS 🦋

• PID — process ID 🪪
• NAME — process name 🫶
• CPU — CPU ID 🖥️
• REFERENCE — number of cache reference events 📈
• MISS — number of cache miss events 💀
• HIT% — cache hit ratio 🔥

🌈 SOURCE 🌈

this is from bcc 💖

https://github.com/iovisor/bcc

also look in the bcc distribution for a companion _examples.txt file. it has example usage, output, and commentary for this tool, so it's a must-read 📚✨

🌷 OS 🌷

Linux 🐧

🥺 STABILITY 🥺

Unstable — still in development 🚧 so vibe check before you rely on it for anything important 🙈

💜 AUTHOR 💜

Teng Qin 👩‍💻🫶

🦋 SEE ALSO 🦋

perf can be used as a generic event counter tool too 🔍 an example for LLC:

# perf top -e cache-misses -e cache-references -a -ns
pid,cpu,comm

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bestie that's the whole tea ☕🎀 this page is from the USER COMMANDS section, dated 2015-08-18, and it's all about llcstat(8) 💖 stay cute, stay curious, and go catch those cache misses 🧚✨💅