July 28, 2026
Kernel drama, now with receipts
How Do I Profile eBPF Code?
Techies turn a tiny file test into a full-blown comment war over hidden slowdowns
TLDR: The post shows how to time file-opening before and after adding low-level monitoring code to see if it slows the system down. Commenters agreed measuring matters, but argued over what really causes slowdowns, with warnings about hidden memory costs, paper-dropping experts, and a random meme stealing the show.
A seemingly simple post about checking whether an extra system monitor slows down file opening somehow turned into performance nerd reality TV. The article itself is practical: build a tiny test program, open the same file again and again, throw away the first warm-up results, and compare the timing before and after adding an eBPF hook. In plain English, it’s a way to catch whether your fancy kernel-level code is secretly making everyday computer tasks drag.
But the comments? That’s where the temperature shot up. One camp came in with receipts, dropping research papers and extra tools like they were entering a boss battle fully geared up. Another commenter delivered the scariest warning in the thread: eBPF is “not magical,” and in one real-world case, more than 90% of the time was allegedly spent stumbling through memory lookups, causing pain far beyond the code being tested. Translation: what looks clever can become everyone else’s problem.
Then the thread took a classic internet turn into comedy. One drive-by comment simply declared, “Lob and Mob,” which reads like either a joke, a spell, or an inside meme nobody wants to explain. Meanwhile, another user rolled in with a brand-new profiler tool called “brr,” basically saying, "Cute benchmark, but if you want the full drama, I’ve got the spotlight." The vibe was clear: yes, measure carefully—but the crowd is deeply split between methodical science, tool flexing, and meme chaos.
Key Points
- •The article uses a minimal C benchmark to measure file-open latency and compare performance before and after attaching an eBPF hook.
- •The benchmark reduces measurement noise by reopening the same file under warm-cache conditions, preallocating and locking memory, and discarding the first 10% of results as warmup.
- •It directly invokes `syscall(SYS_openat, ...)` instead of the libc wrapper to minimize extra overhead in the measured path.
- •To let perf resolve JIT-compiled BPF symbols, the article enables `net.core.bpf_jit_enable=1` and `net.core.bpf_jit_kallsyms=1` and verifies symbols with `bpftool` and `/proc/kallsyms`.
- •The baseline measurement example pins execution to CPU 3, assigns high real-time priority, opens `/etc/hostname` 100,000 times, and writes 90,000 post-warmup samples for later p50/p99 analysis.