In that former article I mentioned two frustrations with the UX301LAA ultrabook that I use as my main production issue: some Iris Graphics text rendering issues and a situation where the ultrabook will randomly reboot... Most of the time the system will just be idling and I'll walk back to the system a few minutes later to find it's rebooted itself. The Iris Graphics issue ended up being a Intel DRM kernel bug that's now fixed prior to 3.15 final. The rebooting issue, meanwhile, appears to be thermal-related after running into the situation several more times.
Since the former article, a few times when the system reboots within one second of the system being powered up via the dmesg for the CPU cores it is already reporting "Core temperature above threshold, cpu clock throttled." Thermal problems were one of my assumptions early on and it's only further enforced by seeing these recent dmesg reports. This is rather surprising though seeing as when these reboots are occurring, the system is generally idling or just having Firefox, the GNOME Terminal, and Thunderbird open on the Ubuntu 14.04 desktop.
What I'm doing now to try to reduce the frequency of these random reboots is forcing the P-State power-save CPU scaling governor to keep the Intel Core i7-4558U statically at its lowest power-state (prior to this I was using the performance/ondemand defaults of P-State and ACPI CPUfreq depending upon the kernel release/configuration tested). Obviously this means reduced performance, but is suffice so far considering the lightweight tasks most of the time from my main production system being writing, Internet use, and emails.
After contacting ASUS after reporting the initial problems via Twitter, their response I received was:
Thank you for reaching out.
I was able to take a look at the service records for this model and I was not able to see anything that would indicate a known hardware issue with it. I do see some calls from our call center records reporting a restarting issue, but it's really nothing out of the ordinary, especially when factoring how well this unit sold.
That temp. range [65~75C] should be normal for these slim ultrabooks so I don't think there's an issue there either.
I'm not especially familiar with Linux troubleshooting, unfortunately. I can say with confidence that there are no known issues with the unit according to our call center records and HQ.
I wouldn't rule out a hardware issue, though; although it might just be isolated to your unit.
I'll see how the Zenbook is working after a few more days of sticking to the powersave scaling governor to keep the CPU in its lowest power/frequency state, but all indications so far are that it's a thermal issue -- either a hardware issue with the device or the Linux driver having too low of a threshold, considering these issues are coming up while idling / minimal load and in an air conditioned environment. Meanwhile, I still haven't encountered these CPU thermal throttling reports or stability issues on my other ASUS Zenbook, the UX32VDA that is being benchmarked quite often under various Linux distributions and different kernels.
Given this ASUS ultrabook is only a few months old, hopefully the ultrabook will be able to work out fine until the mobile Broadwell processors hit the market when I decide on my next laptop/ultrabook or end up back with a MacBook Pro.
Stay tuned for any further updates for this ASUS Zenbook Prime with Ubuntu 14.04 Linux...