Sylvestre Ledru
e173c24599
Mostly mechanical: `markdownlint-cli2 --fix` over the directories the md
linter covers (blank lines around fences and lists, list indentation, bare
URLs wrapped in angle brackets, stray spaces inside code spans).
A few spots needed to be fixed by hand because they were malformed in the
first place: reference links left dangling by the RST conversion in
ipc/docs/ipdl.md and devtools/docs/user/debugger-api/index.md, an `{image}`
directive whose options had escaped the fence in
docs/contributing/debugging/capturing_minidump.md, and text where a literal
asterisk or underscore was being parsed as emphasis.
Differential Revision: https://phabricator.services.mozilla.com/D315001
1.7 KiB
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 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
-noption combined with themach_kernel::wakeupselects a probe point.mach_kernelis the module name andwakeupis the probe name. You can see a complete list of probes by runningsudo 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;
ustackis 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 from FreeBSD.
- DTrace tools, by Brendan Gregg.