Arch Linux

yohanesu75

Member

Registered: 2015-08-21

Posts: 7

[SOLVED] CPU ticks slower and slower on Intel Atom Z3735F

Hi

I have install Arch on Zotac PI320 and I am having some weird problem with CPU speed.

Most starts it runs as normal but sometimes (I think mostly when the device has been powerless) the CPU run slow, and as times passes it get slower and slower. Soon after boot, "sleep 1" takes about 2 seconds but after about 5 minutes "sleep 1" takes 5-10 seconds and gets slower with time.

Anyone familiar with this? I could really need some hints on how to fix this..

I have compared dmesg output from when it runs normal and when its slowing down but I can not find any difference.

Don't know if its related but the computer has a hardware clock with coin battery and I can set time in BIOS but Arch reports there is no RTC.

Edit:
Perhaps related post: https://bbs.archlinux.org/viewtopic.php?id=194422

Last edited by yohanesu75 (2015-08-22 02:09:36)

mich41

Member

Registered: 2012-06-22

Posts: 796

Re: [SOLVED] CPU ticks slower and slower on Intel Atom Z3735F

Does for i in {1..100000}; do :; done also slow down or is it only the clock?

Maybe try booting with clocksource=hpet (or something else, see /sys/devices/system/clocksource/clocksource0/available_clocksource). Verify with dmesg that the chosen clocksource is really used.

yohanesu75

Member

Registered: 2015-08-21

Posts: 7

Re: [SOLVED] CPU ticks slower and slower on Intel Atom Z3735F

for i in {1..100000}; do :; done does not slow down. What conclusion can be made from this fact?

Last edited by yohanesu75 (2015-08-22 01:08:13)

yohanesu75

Member

Registered: 2015-08-21

Posts: 7

Re: [SOLVED] CPU ticks slower and slower on Intel Atom Z3735F

In available_clocksource I have: refined-jiffies, jiffies and tsc.

refined-jiffies seems to be default.
tsc marked unstable because skew too large.
(according to dmesg)

Setting clocksource to hpet in grub.cfg makes tsc the clocksource. No output about skew too large from dmesg.
I'll report results after I done testing on many reboots.

Last edited by yohanesu75 (2015-08-22 01:16:47)

yohanesu75

Member

Registered: 2015-08-21

Posts: 7

Re: [SOLVED] CPU ticks slower and slower on Intel Atom Z3735F

OK, I think I got some progress.

With none or not valid clocksource in kernel parameters it seems like it randomly decides that tsc is unstable and chooses tsc or refined-jiffies accordingly. Not sure but a couple of reboots shows that whenever refined-jiffies is chosen the cpu slows down. Forcing it to tsc in kernel parameters might be the solution I am looking for.

Edit:
Seems like there might be a pattern. Every other reboot tsc is classed unstable and refined-jiffies are chosen. Setting clocksource=refined-jiffies causes slow down CPU at every boot. Setting clocksource=tsc seems to fix the problem. Thank you very much for pointing me in the right direction!!

Last edited by yohanesu75 (2015-08-22 02:05:50)

mich41

Member

Registered: 2012-06-22

Posts: 796

Re: [SOLVED] CPU ticks slower and slower on Intel Atom Z3735F

for i in {1..100000}; do :; done does not slow down. What conclusion can be made from this fact?

This slowing down would indicate that you have some bizarre problem that really causes the CPU clock to gradually slow down, as opposed to "only" having issues with timekeeping in the kernel which actually was the case.

yohanesu75

Member

Registered: 2015-08-21

Posts: 7

Re: [SOLVED] CPU ticks slower and slower on Intel Atom Z3735F

Alright, I see. Thanks a lot for the explanation. The only question remaining is, why is it behaving like this?...

R00KIE

Forum Fellow

From: Between a computer and a chair

Registered: 2008-09-14

Posts: 4,734

Re: [SOLVED] CPU ticks slower and slower on Intel Atom Z3735F

Alright, I see. Thanks a lot for the explanation. The only question remaining is, why is it behaving like this?...

Given the size of the device, have you considered that it may be related to gradual heating? Have you monitored the cpu tempreature?

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R00KIE
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