powerlog

A single-file Bash tool that shows CPU power / thermal / charging / clock / load state on Linux laptops — as a one-shot report or a live one-line-per-second table.

It pulls everything from sysfs, turbostat, rdmsr and the battery gauge, and focuses on telling you why the CPU is doing what it's doing (which power/thermal limit is active, what the real effective clock is, where the watts are going).

A small personal tool that grew out of chasing down why a Dell XPS 13 kept throttling. See Notes.

Example

$ sudo powerlog -w 1
TIME         MHz busy   pkgW   psys   sysW  restW  pkgT   fan   bl  chgW  SOURCE bat% mode   LIMITER  thr+
22:31:10    1547  12%   4.39    5.1    n/a    n/a   51°C  6096  55%    45  AC     100% bal    none        0
22:31:12    2790  31%   9.88    7.4    n/a    n/a   71°C  6105  55%    45  AC     100% perf   PWR         0
22:31:14    1518  10%   3.92    3.0    6.8    2.9   50°C  5476  55%     -  BATT    98% bal    none        0

$ sudo powerlog            # one-shot detailed report
===== POWER / CHARGING =====
  source        : AC
  battery       : 100%  flow +0.0W  (+charge / -discharge)
  ucsi-source-psy-USBC000:001  online=1 45W
  platform(psys): 6.1 W
  RAPL limits   : PL1=64W  PL2=64W
===== CLOCK =====
  power mode    : balanced  (choices: low-power balanced performance)
  driver/gov    : intel_pstate / powersave
  ...

Usage

powerlog              one-shot detailed report (sections, self-labeled)
powerlog -w [SEC]     periodic: one summary line every SEC seconds (default 1)
powerlog -h           help, including a description of every column

Columns (periodic mode)

col	meaning
MHz	effective core frequency, busy-averaged (turbostat Bzy_MHz) — the clock the cores actually ran at, not the requested one
busy	mean CPU utilization across all cores (%)
pkgW	CPU package power, RAPL (W)
psys	raw RAPL psys domain (W) — see caveat below; shown for completeness, not used in restW
sysW	true whole-system power from battery discharge (W); n/a on AC
restW	sysW − pkgW = non-CPU system power (display + SSD + board + …); battery only
pkgT	package temperature (°C)
fan	fastest fan speed (RPM)
bl	backlight brightness (% of actual_brightness)
chgW	charger PD-contract watts offered by the online USB-C/Mains adapter; - on battery
SOURCE	AC or BATT
bat%	battery charge level
mode	OS power profile (/sys/firmware/acpi/platform_profile): perf, bal, lowpwr, …
LIMITER	active perf cap from IA32_PACKAGE_THERM_STATUS (MSR 0x1b1): PWR (power/RAPL), THERM (Tjmax), PROCHOT (external), none
thr+	package thermal-throttle events since the previous line (delta)

The one-shot report additionally shows RAPL PL1/PL2 limits, all thermal zones, cumulative throttle counts, governor/EPP/base-max clocks, and the top CPU consumers.

Requirements

• Linux with an Intel CPU (uses intel_pstate, intel-rapl, IA32_PACKAGE_THERM_STATUS).
• turbostat (from linux-tools / kernel-tools) — for effective MHz + package/psys watts.
• rdmsr (from msr-tools) — for the LIMITER column.
• Everything degrades gracefully: without these (or without privilege) the affected columns show n/a / ? and MHz falls back to the requested frequency.

Privilege

Effective MHz, package watts and the limiter reason read MSRs/RAPL, which need root:

sudo powerlog -w

To run without sudo, grant the two binaries the capability and relax MSR access:

sudo setcap cap_sys_rawio+ep "$(command -v turbostat)"
sudo setcap cap_sys_rawio+ep "$(command -v rdmsr)"
echo 'KERNEL=="msr[0-9]*", GROUP="msr", MODE="0640"' | sudo tee /etc/udev/rules.d/55-msr.rules
sudo groupadd -f msr && sudo usermod -aG msr "$USER" && echo msr | sudo tee /etc/modules-load.d/msr.conf

Install

install -Dm755 powerlog ~/.local/bin/powerlog

Notes & caveats

A few things this tool learned the hard way on a Dell XPS 13 (9310, Tiger Lake); they're documented here because they're easy to misread:

• psys is not whole-system power on every machine. The RAPL psys domain is only meaningful if the OEM wired the platform power sense. On the XPS 9310 it reads at or below package power (impossible for a true platform sensor), so it's shown raw, for completeness, and never used to derive restW. The honest whole-system number is sysW, taken from battery discharge — which is why sysW/restW are n/a on AC (no trustworthy whole-system sensor while plugged in).

• bl (backlight) depends on HDR mode. With HDR off, the panel is driven by the sysfs LED backend and actual_brightness is the live value. With HDR on, the compositor (Mutter) dims via the GPU color pipeline ("ref-white"), pins the sysfs LED, and bl no longer reflects reality (reads ~100%). On such panels HDR brightness isn't exposed in any sysfs/DRM/D-Bus register at all.

• LIMITER is the most useful column for "why is it slow?": PWR means a power limit (RAPL PL1/PL2, or a charger/EC budget) is holding the clock down — often the real culprit on thin laptops, not temperature. THERM means it actually hit Tjmax.

Portable to most Intel laptops; the machine-specific notes above only affect the interpretation of psys and bl.

License

MIT © Nikolay Bryskin