https://segflow.github.io/tags/strace/Recent content in Strace on SegflowHugoen-usMon, 05 Sep 2022 11:20:00 +0100https://segflow.github.io/post/strace-c-fast-cli/Mon, 05 Sep 2022 11:20:00 +0100https://segflow.github.io/post/strace-c-fast-cli/<p>The CLI was fast. I had benchmarked it on my laptop, on a fresh clone of the repo, and it finished in well under a second. Then a coworker pointed it at a real monorepo, the kind with 30,000 files spread across a few thousand directories, and the thing crawled. Same code, same machine class, just more files. The user-visible work had not changed. The wall clock had.</p> <p>This is the story of the half hour I spent figuring out why, what <code>strace -c</code> showed me, and why I now reach for it before any profiler when something &ldquo;feels slow&rdquo; on Linux.</p> <p>My first instinct was wrong, by the way. I assumed disk. The repo was big, the laptop has an NVMe drive but it is not magic, and &ldquo;more files&rdquo; sounds like &ldquo;more IO.&rdquo; So I ran the program twice in a row, expecting the second run to be fast off the page cache. It was not. Both runs took roughly the same time. Whatever was slow, it was not waiting on the disk.</p>