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#1 2020-11-17 00:33:04

oblib__
Member
Registered: 2020-11-16
Posts: 1

XPS 13 9365 gets stuck at 400MHz

My Dell XPS 13 9365 has recently been getting stuck in a super-low frequency CPU setting. I'm not sure what triggers it because, believe it or not, 400MHz can still run a PC almost well enough not to notice because I do a lot of xpra forwarded remote work. Here's what I've figured out so far.

Normal operation: the CPU cycles up and down from 3.6GHz to 800 MHz. While watching I never see it drop below 800MHz. The cpuinfo says max is 3600000 and min is 400000.
Bad mode: the CPU is locked hard at 400MHz always.

Power settings: cpufreq reports `scaling_driver:intel_pstate` and `scaling_governor:performance` (I've tried powersave as well). I usually measure frequency with `grep MH /proc/cpuinfo`. Here's a pastebin of turbostat output: https://pastebin.com/n8t63pvz

This mode seems to be permanent and I'm in it until I power cycle. That means shutdown/power on, not just reboot. Though I have seen it hit this mode straight off boot before too. I have seen it run as much as a day without getting in this mode.

I have caught it enter the mode twice, and it was when I plugged in a USB-C dock device that supplies PD power and HDMI video. However, I have watched while plugging it in and it doesn't trigger the mode when I'm purposely watching. The one time I caught it within a minute or two of it switching, I dumped my `journalctl` logs, but I don't see anything obvious, though there are some errors and "failed to assign" stuff. See https://pastebin.com/nUYtry8N

I don't believe it's related to Windows. This is a dual-boot machine, and I've carefully turned off (recently as part of debug) Windows Fast Boot. But I don't think it's Windows because it will enter the mode while in Linux, and a power cycle can restore it to normal frequencies again. I don't need to go to Windows and back again or anything.

One other thing worth mentioning, though I hope it's not related. Arch Wiki for this module says: "This model only supports the S0 (s2idle) sleep mode. [3] Change the suspend mode to s2idle by adding the mem_sleep_default=s2idle to the kernel parameters. Note: As of 2018/11/18, this does not seem required anymore: the kernel automatically sets it correctly." -- I had that in my kernel parameter and just removed it. It didn't seem to affect this issue at all.

That's about as much debug as I can think of. Any ideas what to try next?

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#2 2020-11-17 07:31:19

V1del
Forum Moderator
Registered: 2012-10-16
Posts: 11,183

Re: XPS 13 9365 gets stuck at 400MHz

Dells seem weirdly susceptible to this. What I've seen mentioned as helping is completely disconnect it from power (unplug the charger, take the battery out... and waiting a few secs to dissipate any left over charge) and then starting back up again

But in general it seems to be an issue with power surges and how the underlying firmware reacts to it. so that connecting an usb dock triggered this is quite possible. Maybe try a firmware upgrade here.

Last edited by V1del (2020-11-17 07:33:20)

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