Messages in this thread | | | Date | Wed, 8 Apr 2020 12:14:52 +0900 | From | Masami Hiramatsu <> | Subject | Re: perf probe + uprobes missing events |
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Hi Arnaldo,
This seems like a perf (perf's ringbuffer?) issue.
Actually, we can not enable perf and ftrace on same uprobe event yet, but the hit counter (uprobe_profile) works.
1) Setup the event.
$ sudo ./perf probe -x ./perf expr__parse expr:string Added new event: probe_perf:expr__parse (on expr__parse in /home/mhiramat/ksrc/linux/tools/perf/perf with expr:string)
You can now use it in all perf tools, such as:
perf record -e probe_perf:expr__parse -aR sleep 1
$ sudo cat /sys/kernel/debug/tracing/uprobe_profile /home/mhiramat/ksrc/linux/tools/perf/perf expr__parse 0
2) run the test command
$ sudo ./perf trace -e probe_perf:expr_* perf test -F expr 7: Simple expression parser : Ok 0.000 perf/9789 probe_perf:expr__parse(__probe_ip: 94836726971904, expr_string: "1+1")
$ sudo cat /sys/kernel/debug/tracing/uprobe_profile /home/mhiramat/ksrc/linux/tools/perf/perf expr__parse 12
OK, this shows the perf trace command only shows 1 event, but uprobe_event itself hits 12 times.
3) run the test command again
$ sudo ./perf trace -e probe_perf:expr_* perf test -F expr 7: Simple expression parser : Ok 0.000 perf/9847 probe_perf:expr__parse(__probe_ip: 94778335464960, expr_string: "1+1") 0.014 perf/9847 probe_perf:expr__parse(__probe_ip: 94778335464960, expr_string: "FOO+BAR") 0.018 perf/9847 probe_perf:expr__parse(__probe_ip: 94778335464960, expr_string: "(BAR/2)%2") $ sudo cat /sys/kernel/debug/tracing/uprobe_profile /home/mhiramat/ksrc/linux/tools/perf/perf expr__parse 24
Again, the perf trace shows only 3 events, but uprobe event hits +12 times
4) run the test command with ftrace.
$ echo 1 | sudo tee /sys/kernel/debug/tracing/events/probe_perf/enable 1 $ ./perf test -F expr 7: Simple expression parser : Ok $ sudo cat /sys/kernel/debug/tracing/uprobe_profile /home/mhiramat/ksrc/linux/tools/perf/perf expr__parse 36
Hit +12 times and the ftrace shows all events correctly.
$ sudo cat /sys/kernel/debug/tracing/trace # tracer: nop # # entries-in-buffer/entries-written: 24/24 #P:8 # # _-----=> irqs-off # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / delay # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | perf-9883 [003] d... 9287.936678: expr__parse: (0x55ea35ce9e00) expr_string="1+1" perf-9883 [003] d... 9287.936694: expr__parse: (0x55ea35ce9e00) expr_string="FOO+BAR" perf-9883 [003] d... 9287.936699: expr__parse: (0x55ea35ce9e00) expr_string="(BAR/2)%2" perf-9883 [003] d... 9287.936704: expr__parse: (0x55ea35ce9e00) expr_string="1 - -4" perf-9883 [003] d... 9287.936707: expr__parse: (0x55ea35ce9e00) expr_string="(FOO-1)*2 + (BAR/2)%2 - -4" perf-9883 [003] d... 9287.936712: expr__parse: (0x55ea35ce9e00) expr_string="1-1 | 1" perf-9883 [003] d... 9287.936716: expr__parse: (0x55ea35ce9e00) expr_string="1-1 & 1" perf-9883 [003] d... 9287.936719: expr__parse: (0x55ea35ce9e00) expr_string="min(1,2) + 1" perf-9883 [003] d... 9287.936723: expr__parse: (0x55ea35ce9e00) expr_string="max(1,2) + 1" perf-9883 [003] d... 9287.936726: expr__parse: (0x55ea35ce9e00) expr_string="1+1 if 3*4 else 0" perf-9883 [003] d... 9287.936731: expr__parse: (0x55ea35ce9e00) expr_string="FOO/0" perf-9883 [003] d... 9287.936734: expr__parse: (0x55ea35ce9e00) expr_string="BAR/"
It seems that the perf ring buffer returns only early events (since expr_string="1+1" is always shown), so I guess there is a timing issue when the ring buffer is read.
Can we delay the read timing?
Thank you,
-- Masami Hiramatsu <mhiramat@kernel.org>
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