Public bug reported:
Environment
CPU: Intel Core Ultra 7 265KF (Arrow Lake, LGA1851)
Motherboard: Gigabyte Z890 Aorus Elite WiFi7 (BIOS F18)
Memory: G.Skill Trident Z5 CK 48GB DDR5-8200 CUDIMM (XMP 3.0, Gear 2)
OS: Ubuntu 24.04.x (Noble), thermald 2.5.6
Desktop system with tower chassis and aftermarket CPU cooler
Required Package and Release Information
Output of lsb_release -rd:
Description: Ubuntu 24.04.4 LTS
Release: 24.04
Output of apt-cache policy thermald:
thermald:
Installed: 2.5.6-2ubuntu0.24.04.3
Candidate: 2.5.6-2ubuntu0.24.04.5
Version table:
2.5.6-2ubuntu0.24.04.5 500
500 http://us.archive.ubuntu.com/ubuntu noble-updates/main amd64
Packages
*** 2.5.6-2ubuntu0.24.04.3 100
100 /var/lib/dpkg/status
2.5.6-2build2 500
500 http://us.archive.ubuntu.com/ubuntu noble/main amd64 Packages
Summary
On a desktop system with no /etc/thermald/thermal-conf.xml present, thermald
starts in zero-configuration/adaptive mode and aggressively invokes
intel_powerclamp on all CPU cores, injecting idle cycles at approximately 50%
duty cycle across all 20 threads. This occurs even when CPU temperatures are
well within safe operating range (28–32°C observed, high threshold 85°C). The
result is an 85% reduction in memory bandwidth and severe degradation of all
compute workloads.
Steps to Reproduce
Install Ubuntu 24.04 on a desktop system with an Intel Core Ultra 200S (Arrow
Lake) processor
Configure DDR5 memory with XMP 3.0 profile at 8200 MT/s in Gear 2 mode
Boot normally — thermald starts automatically with no platform configuration
file
Run any memory or compute benchmark, or observe general system responsiveness
Expected Behavior
On a desktop system with a functional cooler running at 30°C — 55°C below the
high threshold — thermald should either not activate cooling mechanisms, or at
minimum should not invoke intel_powerclamp when no thermal stress exists. RAPL
(Running Average Power Limit), Intel's built-in hardware power management, is
already handling package power autonomously and correctly without thermald's
intervention.
Observed Behavior
thermald invokes intel_powerclamp immediately at boot regardless of
temperature. All 20 idle_inject kernel threads run at approximately 49% CPU
each, forcibly throttling every core to roughly 50% duty cycle system-wide.
thermald logs Config file /etc/thermald/thermal-conf.xml does not exist on
startup and then proceeds to throttle the system anyway in adaptive mode.
Measured Impact
STREAM Triad memory bandwidth benchmark (100M element array, 20 threads, native
compiled):
With thermald active (default): ~6,500 MB/s
With thermald masked and intel_powerclamp removed: ~76,805 MB/s
Suppression: 85%
FreeCAD parametric model recompute time (real-world workload):
With thermald active: approximately equivalent to a 5-year-old laptop
With thermald masked: 2.5x faster, consistent with hardware specifications
Root Cause
thermald in zero-configuration/adaptive mode applies a thermal management
policy calibrated for mobile/laptop platforms. On Arrow Lake specifically, the
tile-based architecture places the memory controller on a separate SoC tile
(TSMC N6) with its own power domain. Under DDR5-8200 Gear 2 operation, SoC tile
power consumption rises sufficiently to trigger thermald's adaptive policy,
even though CPU core temperatures remain nominal. Without a desktop-specific
thermal-conf.xml, thermald has no way to distinguish this hardware from a
thermally constrained laptop, and responds by invoking powerclamp as a
pre-emptive throttle.
Workaround
bashsudo systemctl stop thermald
sudo systemctl mask thermald
sudo rmmod intel_powerclamp
echo "blacklist intel_powerclamp" | sudo tee
/etc/modprobe.d/blacklist-powerclamp.conf
echo "install intel_powerclamp /bin/false" | sudo tee -a
/etc/modprobe.d/blacklist-powerclamp.conf
sudo update-initramfs -u
Proposed Fix
thermald should detect desktop chassis type via DMI data before enabling
powerclamp-based throttling. At minimum, thermald should refuse to invoke
intel_powerclamp when no thermal-conf.xml is present and CPU temperatures are
below a meaningful threshold (e.g., 60°C). Running in adaptive mode on
unrecognized desktop hardware with no configuration file should produce a
prominent warning and default to a passive/monitoring-only posture rather than
active throttling.
Affects
Confirmed on Ubuntu 24.04 (thermald 2.5.6). Ubuntu 26.04 ships thermald 2.5.11
with no documented change to this behavior.
Related Bugs
LP: #1600599, LP: #1940485
** Affects: thermald (Ubuntu)
Importance: Undecided
Status: New
** Tags: arrow-lake desktop intel-powerclamp performance regression thermald
--
You received this bug notification because you are a member of Ubuntu
Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/2156368
Title:
thermald invokes intel_powerclamp on desktop hardware with no thermal-
conf.xml, suppressing memory bandwidth 85% on Arrow Lake systems
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/thermald/+bug/2156368/+subscriptions
--
ubuntu-bugs mailing list
[email protected]
https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
