Arch Linux

imrehg

Member

From: London, UK

Registered: 2008-04-10

Posts: 108

Website

Processor won't go to C3 state in 2.6.28 kernel until usb.autosuspend

Hi,

  I was trying out the new kernel to give a try to some of the goodies before it arrives in the official core repo. However I noticed a change in behaviour of the system, and want to ask here if it is the same for others as well, before I go filing bug reports and stuff....

  I have an EeePC 8G. When using the stock 2.6.27-ARCH kernel, and checking powertop, when the CPU was idle, it went down to the C3 state very nicely (~100% residency). Powertop suggested enabling usb.autosuspend, but even right after boot, without any fooling around, C3 was the norm....

  I compiled the 2.6.28 kernel using the arch stock .config (only changing the CONFIG_LOCALVERSION_AUTO=n), loading it up with 'make menuconfig' and saving it (so the unknown options will be their defaults), it behaves differently.
  After boot, the processor cannot go lower than the C2 state until I enable usb.autoconfig, then it will drop to C3 state when idle....

The output of lsusb

Bus 005 Device 003: ID eb1a:2761 eMPIA Technology, Inc. EeePC 701 integrated Webcam
Bus 005 Device 002: ID 0cf2:6225 ENE Technology, Inc.
Bus 005 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub

(Basically the built-in webcam, the SD card reader, and the hubs...)

The loaded modules (in 2.6.28, but it's actually fewer then in the 2.6.27) with hwdetect --show-modules:

AGP    : agpgart intel-agp
ACPI   : ac battery button dock processor thermal video
PATA   : pata_acpi ata_generic
SCSI   : scsi_mod sd_mod
SATA   : ahci ata_piix
USB    : usb-storage usbcore ehci-hcd uhci-hcd
NET    : atl2 mac80211 rfkill
INPUT  : evdev joydev psmouse serio_raw
SOUND  : pcspkr snd-mixer-oss snd-pcm-oss snd-hwdep snd-page-alloc snd-pcm snd-timer snd snd-pcsp snd-hda-intel soundcore
VIDEO  : compat_ioctl32 uvcvideo v4l1-compat videodev output
OTHER  : intel-rng i2c-i801 i2c-core led-class eeepc-laptop pci_hotplug shpchp rtc-cmos rtc-core rtc-lib iTCO_vendor_support iTCO_wdt

Does this behaviour how up for anybody else with the new kernel? I guess it is not very good for power saving....

  Cheers,
           Greg