Messages in this thread | | | From | Alexandre Courbot <> | Date | Thu, 7 Nov 2013 17:42:54 +0900 | Subject | Is there a notification mechanism for enabled/disabled trace events? |
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Hi everyone,
Trace events can be enabled through debugfs by e.g. writing '1' into their enable node. This is a very useful feature as some tracing functions can introduce overhead and we only want them active when needed.
There is one additional thing that I would need though, which is to be notified when a given trace event is enabled or disabled.
Here is why: I have a power monitoring hardware that can report how much power is currently used by the system. Having this information correlated with other traces (cpufreq, cpuidle, ...) is very useful ; it can be done by repeatedly scheduling a work that probes the power usage and traces it. The job should only be running when the power monitoring trace event is enabled, but AFAIK there is no way to be notified when it is enabled or disabled. So here are a few questions:
1) Is there such a notification mechanism for trace events that I have missed?
2) If not, is there any objection to having one? I'd say my use-case is not so uncommon and others would certainly benefit from it.
3) What would be the right place to have it? ftrace_event_reg() looks like a good place to call a notifier chain, however I'm not sure where the notifier head should be stored, due to my poor understanding of ftrace.
Any answer/comments greatly appreciated!
Thanks, Alex.
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