[PATCH v2 00/11] perf: support enable and disable commands in stat and record modes

Alexey Budankov
2020-05-06T17:16:18Z

Changes in v2:
- renamed resume and pause commands to enable and disable ones, renamed
CTL_CMD_RESUME and CTL_CMD_PAUSE to CTL_CMD_ENABLE and CTL_CMD_DISABLE
to fit to the appropriate ioctls and avoid mixing up with PAUSE_OUTPUT
ioctl;
- factored out event handling loop into a handle_events() for stat mode;
- separated -D,--delay=-1 into separate patches for stat and record modes;

v1: https://lore.kernel.org/lkml/825a5132-b58d-c0b6-b050-5a6040386ec7@linux.intel.com/

repo: tip of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git perf/core

The patch set implements handling of 'start disabled', 'enable' and 'disable'
external control commands which can be provided for stat and record modes
of the tool from an external controlling process. 'start disabled' command
can be used to postpone enabling of events in the beginning of a monitoring
session. 'enable' and 'disable' commands can be used to enable and disable
events correspondingly any time after the start of the session.

The 'start disabled', 'enable' and 'disable' external control commands can be
used to focus measurement on specially selected time intervals of workload
execution. Focused measurement reduces tool intrusion and influence on
workload behavior, reduces distortion and amount of collected and stored
data, mitigates data accuracy loss because measurement and data capturing
happen only during intervals of interest.

A controlling process can be a bash shell script [1], native executable or
any other language program that can directly work with file descriptors,
e.g. pipes [2], and spawn a process, specially the tool one.

-D,--delay <val> option is extended with -1 value to skip events enabling
in the beginning of a monitoring session ('start disabled' command). --ctl-fd
and --ctl-fd-ack command line options are introduced to provide the tool
with a pair of file descriptors to listen to control commands and reply to
the controlling process on the completion of received commands.

The tool reads two byte control command message from ctl-fd descriptor,
handles the command and optionally replies two bytes acknowledgement message
to fd-ack descriptor, if it is specified on the command line. 'enable'
command is recognized as 'e' character message and 'disable' command is
recognized as 'd' character message both received from ctl-fd descriptor.
Completion message is 'a''\n' and sent to fd-ack descriptor.

example bash script demonstrating simple use case:

#!/bin/bash

ctl_dir=/tmp/

ctl_fifo=${ctl_dir}perf_ctl.fifo
test -p ${ctl_fifo} && unlink ${ctl_fifo}
mkfifo ${ctl_fifo} && exec {ctl_fd}<>${ctl_fifo}

ctl_ack_fifo=${ctl_dir}perf_ctl_ack.fifo
test -p ${ctl_ack_fifo} && unlink ${ctl_ack_fifo}
mkfifo ${ctl_ack_fifo} && exec {ctl_fd_ack}<>${ctl_ack_fifo}

perf stat -D -1 -e cpu-cycles -a -I 1000 \
--ctl-fd ${ctl_fd} --ctl-fd-ack ${ctl_fd_ack} \
-- sleep 40 &
perf_pid=$!

sleep 5 && echo 'e' >&${ctl_fd} && read -u ${ctl_fd_ack} e1 && echo "enabled(${e1})"
sleep 10 && echo 'd' >&${ctl_fd} && read -u ${ctl_fd_ack} d1 && echo "disabled(${d1})"
sleep 5 && echo 'e' >&${ctl_fd} && read -u ${ctl_fd_ack} e2 && echo "enabled(${e2})"
sleep 10 && echo 'd' >&${ctl_fd} && read -u ${ctl_fd_ack} d2 && echo "disabled(${d2})"

exec {ctl_fd_ack}>&- && unlink ${ctl_ack_fifo}
exec {ctl_fd}>&- && unlink ${ctl_fifo}

wait -n ${perf_pid}
exit $?

Script output:

[root@host acme] example
Events disabled
# time counts unit events
1.001101062 <not counted> cpu-cycles
2.002994944 <not counted> cpu-cycles
3.004864340 <not counted> cpu-cycles
4.006727177 <not counted> cpu-cycles
Events enabled
enabled(a)
4.993808464 3,124,246 cpu-cycles
5.008597004 3,325,624 cpu-cycles
6.010387483 83,472,992 cpu-cycles
7.012266598 55,877,621 cpu-cycles
8.014175695 97,892,729 cpu-cycles
9.016056093 68,461,242 cpu-cycles
10.017937507 55,449,643 cpu-cycles
11.019830154 68,938,167 cpu-cycles
12.021719952 55,164,101 cpu-cycles
13.023627550 70,535,720 cpu-cycles
14.025580995 53,240,125 cpu-cycles
disabled(a)
14.997518260 53,558,068 cpu-cycles
Events disabled
15.027216416 <not counted> cpu-cycles
16.029052729 <not counted> cpu-cycles
17.030904762 <not counted> cpu-cycles
18.032073424 <not counted> cpu-cycles
19.033805074 <not counted> cpu-cycles
Events enabled
enabled(a)
20.001279097 3,021,022 cpu-cycles
20.035044381 6,434,367 cpu-cycles
21.036923813 89,358,251 cpu-cycles
22.038825169 72,516,351 cpu-cycles
# time counts unit events
23.040715596 55,046,157 cpu-cycles
24.042643757 78,128,649 cpu-cycles
25.044558535 61,052,428 cpu-cycles
26.046452785 62,142,806 cpu-cycles
27.048353021 74,477,971 cpu-cycles
28.050241286 61,001,623 cpu-cycles
29.052149961 61,653,502 cpu-cycles
disabled(a)
30.004980264 82,729,640 cpu-cycles
Events disabled
30.053516176 <not counted> cpu-cycles
31.055348366 <not counted> cpu-cycles
32.057202097 <not counted> cpu-cycles
33.059040702 <not counted> cpu-cycles
34.060843288 <not counted> cpu-cycles
35.000888624 <not counted> cpu-cycles
[root@host acme]#

[1] http://man7.org/linux/man-pages/man1/bash.1.html
[2] http://man7.org/linux/man-pages/man2/pipe.2.html

---
Alexey Budankov (11):
perf evlist: introduce control file descriptors
perf evlist: implement control command handling functions
perf stat: factor out event handling loop into a function
perf stat: extend -D,--delay option with -1 value
perf stat: implement control commands handling
perf stat: introduce --ctl-fd[-ack] options
perf docs: extend stat mode docs with info on --ctl-fd[-ack] options
perf record: extend -D,--delay option with -1 value
perf record: implement control commands handling
perf record: introduce --ctl-fd[-ack] options
perf docs: extend record mode docs with info on --ctl-fd[-ack] options

tools/perf/Documentation/perf-record.txt | 39 +++++++
tools/perf/Documentation/perf-stat.txt | 40 +++++++
tools/perf/builtin-record.c | 39 ++++++-
tools/perf/builtin-stat.c | 137 ++++++++++++++++-------
tools/perf/builtin-trace.c | 2 +-
tools/perf/util/evlist.c | 103 +++++++++++++++++
tools/perf/util/evlist.h | 18 +++
tools/perf/util/record.h | 4 +-
tools/perf/util/stat.h | 4 +-
9 files changed, 339 insertions(+), 47 deletions(-)

--
2.24.1