Re: [Xen-devel] [PATCH v3] new config option vtsc_tolerance_khz to avoid TSC emulation

[Olaf Hering <olaf@xxxxxxxxx>]

Am Tue, 6 Mar 2018 11:07:54 +0000
schrieb Andrew Cooper <andrew.cooper3@xxxxxxxxxx>:

> > One option to avoid the TSC option is to run domUs with tsc_mode=native.
> > This has the drawback that migrating a domU from a "2.3GHz" class host
> > to a "2.4GHz" class host may change the rate at wich the TSC counter
> > increases, the domU may not be prepared for that.  
> 
> Given that you identify this specifically, why do you think this change
> is safe or sensible in the first place?  If using the options here, time
> will definitely drift in the VM after migrate.

This option is a variant of tsc_mode=default for different hosts,
and tsc_mode=native for identical hosts. I think the tsc_mode can not
be adjusted for running domUs. So it gives some control to the host admin
about how to handle the drift.

Olaf

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