Re: [Xen-devel] [PATCH v2] new config option vtsc_khz_tolerance to avoid TSC emulation

[Olaf Hering <olaf@xxxxxxxxx>]

Am Mon, 05 Mar 2018 06:18:17 -0700
schrieb "Jan Beulich" <JBeulich@xxxxxxxx>:

> >>> On 05.03.18 at 12:35, <olaf@xxxxxxxxx> wrote:  
> 
> One thing I'm missing in the description (or the added documentation)
> is a discussion of the conditions under which it is safe to make use of
> the new setting.

The same rules as tsc_mode=native apply, I think.
xen-tscmode(7) has to be updated as well to cover the new knob.


> > +    case XEN_DOMCTL_set_vtsc_khz_tolerance:
> > +        if ( d == currd )
> > +            ret = -EINVAL;  
> Why? There's e.g. no domain_pause() involved here.

I have thought about that. Now I think that part can be even simpler,
just like the following XEN_DOMCTL_suppress_spurious_page_faults:
just change that read-only value unconditionally. There is no obvious
harm in changing that value.

> Also throughout the patch I wonder if it wasn't more natural to
> put the unit last in the parameter / field names.

That was just to keep the diff slightly smaller.


> > +            printk(XENLOG_WARNING "%s: d%u: host has %lu kHz,"
> > +                   " domU expects %u kHz,"
> > +                   " difference of %u is %s tolerance of %u\n",
> > +                   __func__, d->domain_id, cpu_khz, gtsc_khz, khz_diff,
> > +                   diff_tolerated ? "within" : "outside", 
> > vtsc_khz_tolerance);  
> Leftover debugging message?

I think it is worth to log that event, perhaps not with WARNING level.


Olaf

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