High CPU usage following exit from a CPU-intensive program

CanCennau · 2017-11-02 09:33:02

I'm currently using a Genesis series pcspecialist laptop (Intel Pentium quad-core processor, integrated Intel HD graphics using xf86-video-intel driver + mesa, 8GB RAM, 500GB HDD). I'm having an issue where occasionally my laptop will slow right down, and use an incredible amount of CPU for even the simplest tasks.

There doesn't seem to be a specific trigger - I've noticed it happens more often after I run and quit a CPU-intensive program through WINE, but it doesn't happen every time I run a CPU intensive program, and occasionally it happens when I'm not. Updating doesn't fix the issue (although occasionally it helps speed things up), neither does rebooting. Swappiness is currently at 10.

Running top when there's an issue shows there's not one specific program that hogs the CPU, but rather everything seems to use that much more when running, and everything runs much slower. Decrypting the hard drive at boot will take ~14s rather than the usual ~3s, booting the desktop environment will spike at 70% of the CPU rather than the usual ~20%, opening Firefox and playing a YouTube video or opening more than one tab will easily max the CPU out, and the video will stutter and stall as if the internet connection isn't strong enough to play it. This is the case both when using the Tor network and when not.

It normally sorts itself out after five or so days, but it does mean I'm unable to use it properly since everything is incredibly slow - I use Google Docs for essay writing, and the slowness causes a delay of about 5s every time I type, and GD often has to stop and reconnect to the server every couple of words.

journalctl boot log from the last time it happened: https://ptpb.pw/Z7q-

(and I promise I don't usually wait a month to update /o\ this time it resolved itself before I had a chance to update)

It's currently running fine now, but does anyone have any ideas on what I should be looking for/where I should be looking/how to fix it when it happens again?

EDIT: Just in case anyone else runs into this issue - this was a heat management issue. My laptop was set up to begin throttling the CPU at around 45-50C, which meant it regularly hit that limit whenever I ran something CPU-intensive. I fixed it by creating a new thermal-conf.xml file and modifying it so that CPU throttling didn't occur until a much higher temperature, using something similar to the example given in the thermal-conf.xml manual.

Last edited by CanCennau (2017-11-25 15:56:01)

mpan · 2017-11-02 12:41:08

A quick guess: heat management problems leading to CPU throttling. Observe sensors and see if any correlation happens.

The second guess, but somewhat contradicted by some of the reported phenomena: misinterpretation of top output. If CPU frequency goes down, which is expected after a heavy task is finished, then less cycles is available to the system to distribute and the remaining tasks take much more considerable part of the remaining pie.

A point-by-point notes on the whole post:

Please don’t use pastebin.com. Sane alternatives include ptpb, which can also be used with pbpst or curl.
Ensure that Google Docs issues are not caused by actual network problems, which coincide with the CPU thing.
Disk decryption at the boot should take neither 14 nor 3 seconds. It should take 0s, because nothing is decrypted at the boot. Decryption is done when the particular piece of encrypted data is needed. Therefore be more clear on what you have meant by “decryption”.

seth · 2017-11-02 13:09:07

Test a single core

echo 'scale=5000; a(1)*4' | time bc -l # fp
echo '2^2^24' | time bc #int

Then see wheter things are slow afterwards and test it again. Compare the times.
You might rather run into memory issues (I/O is far more prone causing epic delays) and maybe also run a sanity check on your disks: https://wiki.archlinux.org/index.php/SMART (as somehow it survives reboots and lasts 5 days - that doesn't sound much like a CPU issue)

CanCennau · 2017-11-02 13:58:19

Apologies, have updated the link, thanks for pointing it out to me, mpan! To be clear on the decryption thing - my system is requires me to decrypt the drive before the LVM partitions are mounted. There's probably an entire definition of "boot" I'm missing here, since I consider(ed?) anything pre-mount to be the laptop "booting up". Anyways, the part between entering the password and the drive decrypting was what I meant.

Thank you both for the help! I'll refer back here when it happens again.

Last edited by CanCennau (2017-11-02 14:00:11)

Arch Linux

#1 2017-11-02 09:33:02

High CPU usage following exit from a CPU-intensive program

#2 2017-11-02 12:41:08

Re: High CPU usage following exit from a CPU-intensive program

#3 2017-11-02 13:09:07

Re: High CPU usage following exit from a CPU-intensive program

#4 2017-11-02 13:58:19

Re: High CPU usage following exit from a CPU-intensive program

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