You are welcome :)
Yes, LatencyTop uses something similar IIRC, via a prctl() hack: it uses
prctl(PR_SET_NAME) to inject up to 16 characters into the comm - and then every perf
event gets that comm. You can utilize that straight away if you need a marker
solution right now.
A cleaner, more generic approach would be a more free-form ASCII event facility for
this: a generic 'user-space triggered event' with injection capabilities.
To inject it, we could put that into a prctl() as well, for easy, single-syscall
access from C. We already have two perf prctls: PR_TASK_PERF_EVENTS_DISABLE,
PR_TASK_PERF_EVENTS_ENABLE - and this would be a third one: PR_TASK_PERF_USER_EVENT.
This would, like the existing perf_event_task_enable()/disable() methods, loop
through current events and inject a string into matching user events.
Ideally i'd like to see basically user-space access to trace_printk(), and proper
integration into /debug/tracing/events/ enumeration and availability - not a
ftrace-specific and admin-only hack like /sys/kernel/debug/tracing/trace_marker is
today.
Would you be interested in helping out with (and testing) such a more generic
approach?
Thanks,
Ingo
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