On Thu, Apr 01, 2021 at 02:15:48PM -0500, Scott Cheloha wrote: > On Sat, Mar 27, 2021 at 02:20:21AM +0000, Stefmorino wrote: > > > Feel free to share your raw data. > > > > Also includes some standard sendbug dumps: https://0x0.st/-qng.tgz > > Thanks! > > TL;DR: > > Two things: > > 1. Could you check whether Linux will use the TSC as a clocksource on > this machine? The dmesg output on any given distribution should > contain lines about the TSC. > > Feel free to use my easy five-step method. You don't even need to > install Linux, we just need to boot installation media and look at > the dmesg: > > A. Grab the latest Alpine Linux ISO: > > $ ftp > https://dl-cdn.alpinelinux.org/alpine/v3.13/releases/x86_64/alpine-standard-3.13.4-x86_64.iso > > B. Write the ISO to a USB key to create your bootable installation media. > > Achtung! Danger! Don't wipe out the wrong disk! Change /dev/sdNc > to match the special device for your USB stick! > > # dd if=alpine-standard-3.13.4-x86_64.iso of=/dev/sdNc bs=1m > > C. Reboot. > > # shutdown -r now > > D. Boot from the USB stick. How you do this varies by device. Log in as > root. The Alpine installation ramdisk has no root password. > > E. Examine the Linux dmesg for lines about the TSC, clocksources: > > # dmesg | egrep -i 'tsc|clocksource' > > 2. Second, is there a more recent BIOS revision for this machine? > Perhaps (assuming this is in fact a BIOS problem) Lenovo is aware > of it and has fixed it. This is unlikely but worth a look. > > Long version: > > I think two points form a pattern. Bear with me. > > Both you and Josh Rickmar (CC'd) have Lenovo laptops with the same CPU > (AMD Ryzen 5 2500U) and the same BIOS (LENOVO version "R0UET78W (1.58 > )" date 11/17/2020). > > Looking at the data here, both machines exhibit the same problem with > the TSC: the APs are all nearly synchronized outside of small > measurement errors while the BSP is way off. > > This makes me wonder whether this is a firmware/BIOS bug. Perhaps the > BIOS is fussing with the TSC on CPU0 before we boot. Is there a new > BIOS revision available from Lenovo? > > I'd also be interested to know if a recent Linux kernel would even use > the TSC on this laptop as a clocksource or if the kernel complains and > falls back to using the HPET. > > There is a little chit-chat here and there about adding support to > OpenBSD for fixing the TSC skew during synchronization at boot/resume. > One way to do this is with the TSC_ADJUST MSR... > > ... but that won't work here in your case. The CPU on this particular > laptop does not have TSC_ADJUST support, so if we wanted to correct > the TSC skew we'd have to use WRMSR to modify the TSC directly. > > I'm uncertain about whether using WRMSR to reset the TSC on a given > logical processor is universally supported on all amd64 machines or > if it's a special feature a la the TSC_ADJUST MSR. > > -Scott
Hey, thanks for the reminder to try this out with Linux. Will give it a shot shortly. As for the BIOS, 1.58 is the current version (found here): https://support.lenovo.com/us/en/downloads/ds503790 This same issue was happening with all older BIOS versions that I have used as well.
