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VoVaN
l33t
Joined: 02 Jul 2003
Posts: 688
Location: The Netherlands
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 Posted: Sat Aug 08, 2020 2:53 pm Post subject: [solved] Performance degradation with kernel 5.8 |
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Hello,
After updating kernel from 5.7.12 to 5.8.0-r1 I noticed performance degradation on my desktop:
- kernel compilation time ~26 min instead of ~7
- hdparm -Tt for 5.7
| Code: | /dev/sda2:
Timing cached reads: 25448 MB in 1.99 seconds = 12797.63 MB/sec
Timing buffered disk reads: 1418 MB in 3.00 seconds = 472.19 MB/sec
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- hdparm -Tt for 5.8
| Code: | /dev/sda2:
Timing cached reads: 6686 MB in 1.99 seconds = 3362.73 MB/sec
Timing buffered disk reads: 1422 MB in 3.00 seconds = 473.53 MB/sec
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I'd appreciate any thoughts and thank you in advance!
EDIT: Finally understood why  I've default governor settled to "powersave" and CPU frequency scaling worked perfectly fine. With the new kernels >=5.8 there is more choices for governors, while for kernels <5.8 there was only two powersave and performance. So the new kernel changed behavior of this "powersave" governor, so the CPU frequency is always set to the lowest possible value. The new "ondemand" governor has the same behavior as "powersave" for older kernels. End of the story.
Last edited by VoVaN on Thu Aug 20, 2020 5:02 pm; edited 1 time in total |
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Tony0945
Watchman
Joined: 25 Jul 2006
Posts: 5127
Location: Illinois, USA
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| Posted: Thu Aug 20, 2020 4:59 pm Post subject: |
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Please add [solved] to the title. Just edit the post with the edit button,
And thanks for the info. I'm still on 5.4.48 |
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Banana
Veteran
Joined: 21 May 2004
Posts: 1407
Location: Germany
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CaptainBlood
Advocate
Joined: 24 Jan 2010
Posts: 3638
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| Posted: Thu Aug 20, 2020 7:36 pm Post subject: |
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@VoVan
No such an issue on 5.8.2/powersave @building kernel.
GKrellM installed here though.
No idea what's going wrong.
Surprising assumption onpowersave [<5.8.x] = ondemand [5.8.x], any pointer for explanation?
Thks 4 ur attention, interest & support.
Last edited by CaptainBlood on Thu Aug 20, 2020 10:37 pm; edited 2 times in total |
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Anon-E-moose
Watchman
Joined: 23 May 2008
Posts: 6102
Location: Dallas area
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| Posted: Thu Aug 20, 2020 7:53 pm Post subject: |
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I've used the ondemand governor both in the 5.5 series as well as the 5.8 and haven't noticed any difference in compilation/ebuild times. Actually seems like 5.8 is snappier than the 5.5 series, as well as the system running a degree or two cooler (maybe ryzen improvements)
_________________
PRIME x570-pro, 3700x, 6.1 zen kernel
gcc 13, profile 17.0 (custom bare multilib), openrc, wayland |
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swimmer
Veteran
Joined: 15 Jul 2002
Posts: 1330
Location: Netherlands
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| Posted: Thu Aug 20, 2020 10:49 pm Post subject: |
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No problem with the governor so far ...
But there's no possibility to choose any Processor family other than 'Generic-x86-64' ... despite the 'experimental' use-flag :-/
Checking bugs.gentoo.org I saw that it's already reported and a solution should also be implemented but not on my system (5.8.1). |
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