Re: [PATCH v3] x86/tsc: Disable clocksource watchdog for TSC on recent UV

[Jiri Wiesner <jwiesner@suse.de>]

Hello,

On Tue, Oct 07, 2025 at 11:32:17AM -0500, Dimitri Sivanich wrote:
> Disable clocksource watchdog checking on recent and future UV platforms
> to avoid false positives.
> 
> Commits 'b50db7095fe0 ("x86/tsc: Disable clocksource watchdog for TSC on
> qualified platforms")' and '233756a640be ("Extend watchdog check exemption
> to 4-Sockets platform")' were introduced to avoid an issue where the TSC
> is falsely declared unstable by exempting qualified platforms of up to
> 4-sockets from TSC clocksource watchdog checking.  Extend that exemption
> to include recent and future UV platforms.

I am sorry for being MIA for all this time. Apart from HPE customers who do not follow the instruction to add tsc=nowatchdog to the kernel command line, there is another use case for this patch. It has to do with SUSE's efforts to ship a single image per product for deploying machines in the cloud. HPE UV systems that will be used as bare metal are one of the planned instances. The old implementation of the clocksource watchdog needs to be switched off on those UV systems. So, the intention is to backport this patch to all SLES releases that are in active use in the cloud.

A new implementation of the clocksource watchdog has been merged into the upstream kernel. One of the changes made by the new clocksource watchdog implementation is that reference clocksource reads are made on the boot CPU only. Perhaps, the sgi_rtc clocksource would work well with this implementation. So, testing is needed in order to find out if this patch are any future in the upstream Linux. Dimitri, would you be able to run tests on UV systems to check if the new clocksource watchdog implementation works and the hardware limitations of sgi_rtc do not get in the way?
-- 
Jiri Wiesner
SUSE Labs