Re: [PATCH 0/2] RFC: Precise TSC migration

[Marcelo Tosatti]

On Tue, Dec 01, 2020 at 02:48:11PM +0100, Thomas Gleixner wrote:
> On Mon, Nov 30 2020 at 16:16, Marcelo Tosatti wrote:
> >> Besides, Linux guests don't sync the TSC via IA32_TSC write,
> >> but rather use IA32_TSC_ADJUST which currently doesn't participate
> >> in the tsc sync heruistics.
> >
> > Linux should not try to sync the TSC with IA32_TSC_ADJUST. It expects
> > the BIOS to boot with synced TSCs.
> 
> That's wishful thinking.
> 
> Reality is that BIOS tinkerers fail to get it right. TSC_ADJUST allows
> us to undo the wreckage they create.
> 
> Thanks,
> 
>         tglx

Have not seen any multicore Dell/HP systems require that.

Anyway, for QEMU/KVM it should be synced (unless there is a bug
in the sync logic in the first place).