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# tools/power/rapl
`tools/power/rapl` (or `rapl` for short) is a command-line utility in
the Mozilla tree that periodically reads and prints all available Intel
RAPL power estimates. These are machine-wide estimates, so if you want
to estimate the power consumption of a single program you should
minimize other activity on the machine while measuring.
**Note**: The [power profiling overview](power_profiling_overview.md) is
worth reading at this point if you haven't already. It may make parts
of this document easier to understand.
## Invocation
First, do a [standard build of Firefox](/setup/index.rst).
### Mac
On Mac, `rapl` can be run as follows.
```bash
$OBJDIR/dist/bin/rapl
```
### Linux
On Linux, `rapl` can be run as root, as follows.
sudo $OBJDIR/dist/bin/rapl
Alternatively, it can be run without root privileges by setting the
contents of
[/proc/sys/kernel/perf_event_paranoid](
http://unix.stackexchange.com/questions/14227/do-i-need-root-admin-permissions-to-run-userspace-perf-tool-perf-events-ar)
to
0. Note that if you do change this file, its contents may reset when
the machine is next rebooted.
You must be running Linux kernel version
3.
14 or later for `rapl` to
work. Otherwise, it will fail with an error message explaining this
requirement.
### Windows
Unfortunately, `rapl` does not work on Windows, and porting it would be
difficult because Windows does not have APIs that allow easy access to
the relevant model-specific registers.
## Output
The following is
10 seconds of output from a default invocation of
`rapl`.
```bash
total W = _pkg_ (cores + _gpu_ + other) + _ram_ W
#
01 5.
17 W =
1.
78 (
0.
12 +
0.
10 +
1.
56) +
3.
39 W
#
02 9.
43 W =
5.
44 (
1.
44 +
1.
20 +
2.
80) +
3.
98 W
#
03 14.
26 W =
10.
21 (
5.
47 +
0.
19 +
4.
55) +
4.
04 W
#
04 10.
02 W =
6.
15 (
2.
62 +
0.
43 +
3.
10) +
3.
86 W
#
05 14.
63 W =
10.
43 (
4.
41 +
0.
81 +
5.
22) +
4.
19 W
#
06 11.
16 W =
6.
90 (
1.
91 +
1.
68 +
3.
31) +
4.
26 W
#
07 5.
40 W =
1.
97 (
0.
20 +
0.
10 +
1.
67) +
3.
44 W
#
08 5.
17 W =
1.
76 (
0.
07 +
0.
08 +
1.
60) +
3.
41 W
#
09 5.
17 W =
1.
76 (
0.
09 +
0.
08 +
1.
58) +
3.
42 W
#
10 8.
13 W =
4.
40 (
1.
55 +
0.
11 +
2.
74) +
3.
73 W
```
Things to note include the following.
- All measurements are in Watts.
- The first line indicates the meaning of each column.
- The underscores in `_pkg_`, `_gpu_` and `_ram_` are present so that
each column's name has five characters.
- The total power is the sum of the package power and the RAM power.
- The package estimate is divided into three parts: cores, GPU, and
\"other\". \"Other\" is computed as the package power minus the
cores power and GPU power.
- If the processor does not support GPU or RAM estimates then
\"` n/a `\" will be printed in the relevant column instead of a
number, and it will contribute zero to the total.
Once sampling is finished --- either because the user interrupted it, or
because the requested number of samples has been taken --- the following
summary data is shown:
```bash
10 samples taken over a period of
10.
000 seconds
Distribution of 'total' values:
mean =
8.
85 W
std dev =
3.
50 W
0th percentile =
5.
17 W (min)
5th percentile =
5.
17 W
25th percentile =
5.
17 W
50th percentile =
8.
13 W
75th percentile =
11.
16 W
95th percentile =
14.
63 W
100th percentile =
14.
63 W (max)
```
The distribution data is omitted if there was zero or one samples taken.
## Options
- `-i --sample-interval`. The length of each sample in milliseconds.
Defaults to
1000. A warning is given if you set it below
50 because
that is likely to lead to inaccurate estimates.
- `-n --sample-count`. The number of samples to take. The default is
0, which is interpreted as \"unlimited\".
## Combining with `powermetrics`
On Mac, you can use the [mach power](powermetrics.md#mach-power) command
to run `rapl` in combination with `powermetrics` in a way that gives the
most useful summary measurements for each of Firefox, Chrome and Safari.
