Re: [PATCH] replace rdtsc emulation-vs-native xen boot option with per-domain (hypervisor part)

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 10/05/09 18:43, Dan Magenheimer wrote:
> Perhaps a better choice would be for emulated tsc
> to return Xen system time in both kernel and user
> mode (which is what it does for HVM domains) and,
> when a domain has tsc_native==0,
> Xen sets its pvclock parameters so that no scaling
> occurs?  This results in the guest reporting that
> it has a 1GHz clock, but may be more consistent.
>   

Yes, as I said:
> But aside from that, all I'm asking for is a way for a domain to
> explicitly request that its tsc not be synthesized (or failing that,
> something that looks exactly like an unsynthesized tsc), so that
> usermode pvclock can work without needing edits to the config file.
>   

Having a consistent tsc between usermode and kernel will solve the
significant functional breakage that currently exists with tsc synthesis
enabled, making it just a question of performance (and resolution).

I still think tsc_native=1 is the correct setting for the vast majority
of PV guest domains, and enabling it by default is a bad idea.

    J