From 36d22d82aa202bb199967e9512281e9a53db42c9 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 21:33:14 +0200 Subject: Adding upstream version 115.7.0esr. Signed-off-by: Daniel Baumann --- docs/performance/dtrace.md | 49 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) create mode 100644 docs/performance/dtrace.md (limited to 'docs/performance/dtrace.md') diff --git a/docs/performance/dtrace.md b/docs/performance/dtrace.md new file mode 100644 index 0000000000..68e5114297 --- /dev/null +++ b/docs/performance/dtrace.md @@ -0,0 +1,49 @@ +# dtrace + +`dtrace` is a powerful Mac OS X kernel instrumentation system that can +be used to profile wakeups. This article provides a light introduction +to it. + +::: +**Note**: The [power profiling overview](power_profiling_overview.md) is +worth reading at this point if you haven't already. It may make parts +of this document easier to understand. +::: + +## Invocation + +`dtrace` must be invoked as the super-user. A good starting command for +profiling wakeups is the following. + +``` +sudo dtrace -n 'mach_kernel::wakeup { @[ustack()] = count(); }' -p $FIREFOX_PID > $OUTPUT_FILE +``` + +Let's break that down further. + +- The` -n` option combined with the `mach_kernel::wakeup` selects a + *probe point*. `mach_kernel` is the *module name* and `wakeup` is + the *probe name*. You can see a complete list of probes by running + `sudo dtrace -l`. +- The code between the braces is run when the probe point is hit. The + above code counts unique stack traces when wakeups occur; `ustack` + is short for \"user stack\", i.e. the stack of the userspace program + executing. + +Run that command for a few seconds and then hit [Ctrl]{.kbd} + [C]{.kbd} +to interrupt it. `dtrace` will then print to the output file a number of +stack traces, along with a wakeup count for each one. The ordering of +the stack traces can be non-obvious, so look at them carefully. + +Sometimes the stack trace has less information than one would like. +It's unclear how to improve upon this. + +## See also + +dtrace is *very* powerful, and you can learn more about it by consulting +the following resources: + +- [The DTrace one-liner + tutorial](https://wiki.freebsd.org/DTrace/Tutorial) from FreeBSD. +- [DTrace tools](http://www.brendangregg.com/dtrace.html), by Brendan + Gregg. -- cgit v1.2.3