With Linux and perf 5.0.0-23-generic (HWE or Hardware Enablement), it is
broken.
Versions
--------
$ uname -r
5.0.0-23-generic
$ perf --version
perf version 5.0.15
$ dpkg -l|grep 5.0.0-23|awk '{print $1,$2,$3,$4}'|column -t
ii linux-headers-5.0.0-23 5.0.0-23.24~18.04.1 all
ii linux-headers-5.0.0-23-generic 5.0.0-23.24~18.04.1 amd64
ii linux-hwe-tools-5.0.0-23 5.0.0-23.24~18.04.1 amd64
ii linux-image-5.0.0-23-generic 5.0.0-23.24~18.04.1 amd64
ii linux-modules-5.0.0-23-generic 5.0.0-23.24~18.04.1 amd64
ii linux-modules-extra-5.0.0-23-generic 5.0.0-23.24~18.04.1 amd64
ii linux-tools-5.0.0-23-generic 5.0.0-23.24~18.04.1 amd64
A minimal series of steps necessary to make it happen
-----------------------------------------------------
1. In a terminal tab., run:
$ top
2. In another tab, run
$ perf top -p `pidof top`
3. Look at the output of "perf top".
What you expected to happen
---------------------------
I expect to see "cycles" events being reported for the process "top"
(started at step 1.)
See section "What actually happened" in comment #1 above.
What actually happened
----------------------
The output of "perf top -p `pidof top`" (step 2) is:
Samples: 0 of event 'cycles:ppp', 4000 Hz, Event count (approx.): 0 lost: 0/0
drop: 0/0
Overhead
It is as if there are no events being sampled.
System calls
------------
perf_event_open System calls:
$ strace perf top -p `pidof top` 2>&1 | grep ^perf_event_open
perf_event_open({type=PERF_TYPE_HARDWARE, size=PERF_ATTR_SIZE_VER5,
config=PERF_COUNT_HW_CPU_CYCLES, ...}, 0, -1, -1, 0) = 3
perf_event_open({type=PERF_TYPE_SOFTWARE, size=0 /* PERF_ATTR_SIZE_??? */,
config=PERF_COUNT_SW_CPU_CLOCK, ...}, -1, 2, -1, PERF_FLAG_FD_CLOEXEC) = 3
perf_event_open({type=PERF_TYPE_HARDWARE, size=PERF_ATTR_SIZE_VER5,
config=PERF_COUNT_HW_CPU_CYCLES, ...}, -1, 0, -1, PERF_FLAG_FD_CLOEXEC) = 3
perf_event_open({type=PERF_TYPE_HARDWARE, size=PERF_ATTR_SIZE_VER5,
config=PERF_COUNT_HW_CPU_CYCLES, ...}, -1, 0, -1, PERF_FLAG_FD_CLOEXEC) = 3
perf_event_open({type=PERF_TYPE_HARDWARE, size=PERF_ATTR_SIZE_VER5,
config=PERF_COUNT_HW_CPU_CYCLES, ...}, 4035, -1, -1, PERF_FLAG_FD_CLOEXEC) = 3
Additional note
---------------
Using the full path to perf 5.0.0-23 also produce 0 events.
$ /usr/lib/linux-tools/5.0.0-23-generic/perf top -p `pidof top`
--
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Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/1839852
Title:
perf broken on hwe kernel 5.0.0-23
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