December 18, 2025
Yo dawg, we profiled a profiler
From profiling to kernel patch: the journey to an eBPF performance fix
Paid profiler triggers Linux speed-up; comments go wild
TLDR: A paid CPU profiler uncovered a slowdown in Linux’s eBPF updates and helped land a kernel fix that speeds things up. Commenters loved the meta moment but argued over paywalls, opt-in controls, and whether users misused features—still, faster profiling for everyone is a win.
A routine “profile the profiler” moment turned into a Linux glow-up: Superluminal, a paid CPU profiler, used kernel add-on eBPF (tiny safe programs that run inside Linux) and found a slowdown when updating “maps inside maps.” The result? A kernel patch that makes those updates much faster—and the comments instantly lit up. Some cheered the sheer nerd poetry of profiling the profiler (yo dawg, anyone?) and called it a slick demo that could help everyone using eBPF, not just paying customers. Others side-eyed the price tag and asked why a fix discovered by a commercial tool should drive kernel changes. The spiciest thread came from a fan who still dragged the rollout: making a “sync point” paid for all users was called a mistake, with demands for an opt-in switch. That same commenter threw shade at folks who “mis-used the eBPF map,” sparking a mini culture war: is it user error or bad design if people trip over a feature? Meanwhile, jokesters dubbed map-in-map “Kernel Inception” and begged for a sequel: profile the patch that fixed the profiler. Drama aside, the community agrees the speed boost matters—faster performance data means smoother apps and fewer headaches for anyone peeking under the hood of Linux
Key Points
- •Superluminal’s Linux CPU profiler uses eBPF to collect performance events via kernel hooks like tracepoints, kprobes, and perf events.
- •Data is exchanged between kernel eBPF programs and userspace through eBPF maps; a ring buffer map streams events to userspace.
- •Unwind data extracted from .eh_frame is converted to an internal format and uploaded to eBPF using BPF_MAP_TYPE_ARRAY_OF_MAPS via bpf_map_update_elem.
- •To reduce startup latency, unwind data is precached by enumerating binaries and uploading per-binary data before profiling begins.
- •Profiling revealed bottlenecks in map-in-map updates, culminating in a Linux kernel change that speeds up these updates.