Re: TSC x86 fixes for LTS kernel 4.9.x

[Greg KH]

On Wed, Dec 13, 2017 at 10:33:52AM +0200, Dan Aloni wrote:
> Hi all,
> 
> I've tested the following changes, belonging to merge commit f7dd3b1734e,
> on top of 4.9.68 after a very easy backport from 4.10, and I think it
> may be worthwhile adding them to 4.9.x:
> 
>       x86/tsc: Limit the adjust value further
>       x86/tsc: Annotate printouts as firmware bug
>       x86/tsc: Force TSC_ADJUST register to value >= zero
>       x86/tsc: Validate TSC_ADJUST after resume
>       x86/tsc: Validate cpumask pointer before accessing it
>       x86/tsc: Fix broken CONFIG_X86_TSC=n build
>       x86/tsc: Try to adjust TSC if sync test fails
>       x86/tsc: Prepare warp test for TSC adjustment
>       x86/tsc: Move sync cleanup to a safe place
>       x86/tsc: Sync test only for the first cpu in a package
>       x86/tsc: Verify TSC_ADJUST from idle
>       x86/tsc: Store and check TSC ADJUST MSR
>       x86/tsc: Detect random warps
>       x86/tsc: Use X86_FEATURE_TSC_ADJUST in detect_art()
>       x86/tsc: Finalize the split of the TSC_RELIABLE flag
>       x86/tsc: Set TSC_KNOWN_FREQ and TSC_RELIABLE flags on Intel Atom SoCs
>       x86/tsc: Mark Intel ATOM_GOLDMONT TSC reliable
>       x86/tsc: Mark TSC frequency determined by CPUID as known
>       x86/tsc: Add X86_FEATURE_TSC_KNOWN_FREQ flag

I need git commit ids to be able to do anything :)

> These changes percisely fix an issue I am having with a relatively new
> 8-core Intel(R) Core(TM) i7-7820X with an updated ASUS BIOS (December 2017).
> 
> Under v4.9.68, the kernel fallbacks on the chosen clocksource to HPET which
> just doesn't work - there is over a 200ms time drift that does not go
> away even after repeated ntpdate sync attempts.
> 
> For further testing I've posted a branch for these changes here:
> 
>     https://github.com/kernelim/linux tsc-fix-for-4.9.x

Why not just use 4.14 instead?  That's much easier than trying to use an
old kernel like 4.9, right?

thanks,

greg k-h