[Qemu-devel] Static tracepoint control via trace-event

[Jan Kiszka <jan.kiszka@siemens.com>]

Hi Stefan,

just had a closer look at qemu's new tracing framework. Looks cool,
though it leaves a bit room for improvements. ;)

One quirk I stumbled over quickly was the "disable" tag in trace-events.
It confused me first as qemu starts without any tracepoint enabled by
default and I thought I had to hack the file. Then I read the doc and
wondered which exiting or future backend would come without sufficiently
fast dynamic tracepoint control. Do you have any in mind?

Instead of making it a compile-time switch (except for simpletrace), I
would vote for declaring the simpletrace usage as the only one: disable
sets the default state of the dynamic tracepoint. That way we could use
trace-events to define a useful set of standard, moderate-impact
tracepoints that shall be on. Others will still be available once a
backend is configured, but remain off until enabled during runtime.
Anything else looks like overkill to me.

There are a few more things I have in mind (ftrace backend, enhanced
"-trace" switch, wildcards for enabling tracepoints, and more
tracepoints). Will hopefully come up with patches to address them, but
this may take a while.

Jan

PS: Do you maintain a tracing git tree?

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