Simon Willison’s Weblog

Did you know about Instruments? (via) Thorsten Ball shows how the macOS Instruments app (installed as part of Xcode) can be used to run a CPU profiler against any application - not just code written in Swift/Objective C.

I tried this against a Python process running LLM executing a Llama 3.1 prompt with my new llm-gguf plugin and captured this:

# 26th July 2024, 1:06 pm / observability, profiling, python

Making Code Faster. Tim Bray’s detailed guide to using the Go profiler.

# 13th June 2022, 7:40 pm / profiling, go, tim-bray

How I cut GTA Online loading times by 70% (via) Incredible debugging war story: t0st was fed up of waiting six minutes (!) for GTA Online to load on their PC, so they used a host of devious debugging tricks to try and figure out what was going on. It turned out the game was loading a 10MB JSON file detailing all of the available in-game purchases, but inefficient JSON parsing meant it was pegging an entire CPU for 4 minutes mainly running the strlen() C function. Despite not having access to source code or debugging symbols t0st figured out the problem and managed to inject a custom DLL that hooked some internal functions and dropped load times down from 6m down to to 1m50s!

# 1st March 2021, 7:12 pm / profiling, hacking, debugger

Using memory-profiler to debug excessive memory usage in healthkit-to-sqlite. This morning I figured out how to use the memory-profiler module (and mprof command line tool) to debug memory usage of Python processes. I added the details, including screenshots, to this GitHub issue. It helped me knock down RAM usage for my healthkit-to-sqlite from 2.5GB to just 80MB by making smarter usage of the ElementTree pull parser.

# 24th July 2019, 8:25 am / memory, xml, profiling, python, elementtree

Using flamegraphs. I really like flamegraphs as a profiling tool—we have support for them baked into our Tikibar debugging toolbar at Eventbrite—but interpreting them isn’t particularly intuitive on first glance. Julia Evans has put together a great explanation of how to read them as part of the documentation for her rbspy Ruby profiler.

# 21st March 2018, 8:56 pm / profiling, julia-evans

profiling. “An interactive continuous Python profiler”. This is really neat—simply run “profiling myscript.py” to get an interactive, navigable console-based profile inspector at the end of your script... or run “profiling live-profile mywebverver.py” to see a live, updating profile of a long-running process. Has options for statistical profiling as well, which has a much lower overhead in exchange for a less accurate view of what is going on.

# 28th October 2017, 1:06 am / profiling, python

Building a statistical profiler in python. Generating flame graphs of production Python code is surprisingly straight-forward. Brian Pitts built a statistical flame graph profiler into our tikibar debugging tool at Eventbrite and it’s proved extremely useful.

# 5th October 2017, 3:44 pm / profiling, tikibar, django, python

How to find un-indexed queries in MySQL, without using the log (via) Use tcpdump(!) to sniff the MySQL protocol and dump out queries that had the “no index used” bit set.

# 19th August 2009, 11:42 am / tcpdump, mysql, profiling

Building a Better JavaScript Profiler with WebKit. Clever hack from Francisco Tolmasky which solves the problem of JavaScript profilers showing ? as the name of any anonymous functions. He patched the WebKit profiler to look for a displayName attribute on a function and show that as the function name instead.

# 29th April 2009, 11:57 pm / webkit, profiling, javascript, franciscotolmasky

Heap Dump Analysis. Using jmap to dump the JVM’s memory to disk, then analysing it using the visualvm GUI tool.

# 2nd April 2009, 10:34 am / java, jvm, profiling, heapdump, memory, visualvm, dominicmitchell

Using the New MySQL Query Profiler. Extremely powerful new feature in MySQL 5.0.37. Definitely something for the Django debug toolbar.

# 1st October 2008, 1:20 am / django-debug-toolbar, django, mysql, profiling

Deep Profiling jQuery Apps. Neat plugin from John Resig that monkey-patches most (all?) of the jQuery methods to build up a detailed profile of which methods are being used by a given page.

# 16th June 2008, 10:20 am / jquery, javascript, profiling, john-resig

YSlow: Bug (fix) in Firebug’s Net Panel. The latest release of the YSlow page analysis plugin (announced at FOWA) also fixes a misleading bug in Firebug’s Net panel.

# 5th October 2007, 10:26 pm / steve-souders, firefox, firebug, fowa, yslow, yahoo, profiling