I'm using Ubuntu 13.04 dev and have noticed a high cpu overhead if a process is using multiple threads and computing them on different cores. To measure this I have written a little script in Python which I will attach.
The script will create 2 threads which are using only a little time of a cpu core. On my AMD Phenom II X6 1045T the Linux kernel will assign the 2 threads on 2 cores which will use a total cpu time of 40% from a maximum of 600%. But if I'm using "taskset -ap 0x00000001 pid_of_script" the 2 threads will be assigned to 1 core and the total cpu usage will be only 25% from 600%.
I'm wondering why there is a cpu overhead of 60% if the Linux kernel is using 2 cores instead of 1 core.
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AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.25.
AplayDevices:
**** List of PLAYBACK Hardware Devices ****
card 0: SB [HDA ATI SB], device 0: ALC662 rev1 Analog [ALC662 rev1 Analog]
Subdevices: 0/1
Subdevice #0: subdevice #0
ApportVersion: 2.6.1-0ubuntu6
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: sworddragon 2374 F.... plugin-containe
/dev/snd/pcmC0D0p: sworddragon 2374 F...m plugin-containe
/dev/snd/timer: sworddragon 2374 f.... plugin-containe
CRDA: Error: [Errno 2] No such file or directory
Card0.Amixer.info:
Card hw:0 'SB'/'HDA ATI SB at 0xf9ff4000 irq 16'
Mixer name : 'Realtek ALC662 rev1'
Components : 'HDA:10ec0662,18497662,00100101'
Controls : 33
Simple ctrls : 18
CurrentDmesg:
Error: command ['sh', '-c', 'dmesg | comm -13 --nocheck-order /var/log/dmesg -'] failed with exit code 1: comm: /var/log/dmesg: No such file or directory
dmesg: write failed: Broken pipe
DistroRelease: Ubuntu 13.04
EcryptfsInUse: Yes
IwConfig: Error: [Errno 2] No such file or directory
Lsusb: Error: [Errno 2] No such file or directory
MachineType: To Be Filled By O.E.M. To Be Filled By O.E.M.
MarkForUpload: True
NonfreeKernelModules: nvidia
Package: linux (not installed)
ProcEnviron:
TERM=xterm
PATH=(custom, no user)
LANG=de_DE.UTF-8
SHELL=/bin/bash
ProcFB: 0 VESA VGA
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.5.0-17-generic root=UUID=f1ce7323-74dc-46f7-95f7-887cc54403e7 ro
ProcVersionSignature: Ubuntu 3.5.0-17.28-generic 3.5.5
RfKill: Error: [Errno 2] No such file or directory
Tags: raring
Uname: Linux 3.5.0-17-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dialout lpadmin plugdev sambashare sudo
dmi.bios.date: 05/21/2012
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: P1.20
dmi.board.asset.tag: BC5FF4739C55
dmi.board.name: 960GM/U3S3 FX
dmi.board.vendor: ASRock
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: To Be Filled By O.E.M.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrP1.20:bd05/21/2012:svnToBeFilledByO.E.M.:pnToBeFilledByO.E.M.:pvrToBeFilledByO.E.M.:rvnASRock:rn960GM/U3S3FX:rvr:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.:
dmi.product.name: To Be Filled By O.E.M.
dmi.product.version: To Be Filled By O.E.M.
dmi.sys.vendor: To Be Filled By O.E.M.
This bug is missing log files that will aid in diagnosing the problem. From a terminal window please run:
apport-collect 1073148
and then change the status of the bug to 'Confirmed'.
If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.
This change has been made by an automated script, maintained by the Ubuntu Kernel Team.