Re: [Xen-devel] [PATCH v5] new config option vtsc_tolerance_khz to avoid TSC emulation

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Mar 29, 2018 at 10:58:34AM +0200, Olaf Hering wrote:
> On Thu, Mar 29, Roger Pau Monné wrote:
> 
> > AFAICT in the chunk above you will disable vtsc without checking if
> > the hardware supports TSC scaling, which leads to inaccurate TSC values
> > on hardware that could provide accurate results without the software
> > emulation overhead.
> 
> Is that really the case? Maybe I get the logic wrong, but what I see is:
> what ever my change does, or if a HVM domain runs on a host with scaling
> feature, disable vtsc. hvm_get_tsc_scaling_ratio has no side effects.
> Isnt the purpose to not emulate vtsc if the hardware supports scaling?

Yes, that's correct. I read that wrong an somehow tied the vtsc
setting to the hardware TSC emulation.

IMO it would still be good to mention the relation between the
tolerance and the TSC hardware scaling in the commit message.

Thanks, Roger.

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