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** Also affects: linux (Ubuntu Noble)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Noble)
Status: New => Incomplete
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https://bugs.launchpad.net/bugs/2109897
Title:
CPU does not return to deep C-states (C8–C10) after SATA SSD wakeup
from standby
Status in linux package in Ubuntu:
New
Status in linux source package in Noble:
Incomplete
Bug description:
Description:
After manually configuring my Ubuntu Server 25.04 system for ultra-low power
consumption (idle ~3.2W), I’ve encountered an issue where the CPU no longer
enters deep C-states (C8–C10) after a SATA SSD is woken up from standby (e.g.,
by accessing a file on the drive).
What works (before disk wakeup):
CPU reaches deep C-states C8, C9, C10 reliably
SATA SSD (crusial CT1000MX) is set to standby via hdparm -y
System stays in ultra-low idle power (~3.2W)
What breaks (after wakeup):
After any disk access wakes up the SATA SSD from standby, CPU only goes as
deep as C2
Even after the disk goes back to standby, CPU remains stuck in shallow
C-states (C2 max)
Requires system reboot to recover full C-state entry
What I tried:
Using TLP and powertop to re-apply tunables
Manually re-enabling autosuspend and PCIe ASPM
Checking /sys/devices/system/cpu/cpu*/cpuidle/state*/usage — confirms C8–C10
stop being used
When I switched to Debian Trixie with kernel 6.12.22 there were no such
problems and the system remained idle on C10 all the time despite frequent disk
operations.
System Info:
Ubuntu Server 25.04
Kernel: 6.14.0-15-generic
TLP: 1.8.0 with aggressive power-saving settings
CPU: Intel J6412 (Elkhart Lake), ASPM and C10 enabled in BIOS
SSD: Crusial CT1000MX 1TB (SATA)
How to reproduce:
Boot system and ensure CPU enters deep C-states (via powertop or /sys stats)
Send SATA SSD to standby: hdparm -y /dev/sdX
Wait until system is idle and in deep sleep
Wake disk via file read (e.g., cat /mnt/ssd/file)
Check CPU C-states — C8–C10 no longer used
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