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Subject[RFC] adding of TGID to ftrace output
Hi Steven,

Can we add TGID information along with PID to ftrace output?

Something like:
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID:TGID CPU# |||| TIMESTAMP FUNCTION
# | | | | |||| | |
bash-1977:1977 [000] .... 17284.993652: sys_close <-

Instead of:
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
bash-1977 [000] .... 17284.993652: sys_close <-

Currently in android, we inject tgid into each trace event at the end
of the trace just so we can group threads under a process in our trace
viewer.

The other option we're thinking off is we can retrieve tgid during the
trace output (reading trace file from debugfs/tracefs) from the
task_struct and then have ftrace output it that way.

Anyway, having this will really simplify things and make it more
reliable (we run ps -T at the end of the trace right now, but its
unreliable because threads might have exited by then). We also have to
call getpid() and inject pid into each userspace trace_marker write
just so we can do this grouping.

Regards,
Joel

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