Re: [PATCH v5 6/6] docs: Add descriptions of TSC scaling in xl.cfg and tscmode.txt

["Zhang, Haozhong" <haozhong.zhang@intel.com>]

On 02/29/16 10:02, Tian, Kevin wrote:
> > From: Jan Beulich [mailto:JBeulich@suse.com]
> > Sent: Friday, February 26, 2016 4:01 PM
> > 
> > >>> On 26.02.16 at 05:37, <kevin.tian@intel.com> wrote:
> > >>  From: Zhang, Haozhong
> > >> Sent: Tuesday, February 23, 2016 10:05 AM
> > >>
> > >> Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
> > >
> > > Reviewed-by: Kevin Tian <kevin.tian@intel.com>, except:
> > >
> > >> +
> > >> +Hardware TSC Scaling
> > >> +
> > >> +Intel VMX TSC scaling and AMD SVM TSC ratio allow the guest TSC read
> > >> +by guest rdtsc/p increasing in a different frequency than the host
> > >> +TSC frequency.
> > >> +
> > >> +If a HVM container in default TSC mode (tsc_mode=0) or PVRDTSCP mode
> > >
> > > 'HVM container' means something different. We usually use "HVM domain"
> > > as you may see in other places in this doc.
> > 
> > But I think this is specifically meant to refer to both HVM and PVH
> > domains.
> > 
> 
> First, I have a feeling that many people today refer to containers
> running within a VM as 'VM container', which is a bit confusing to
> 'HVM container' purpose here. Couldn't we use 'HVM domains'
> to cover both HVM and PVH (which is PV-HVM)? Curious whether
> there is formal definition of those terminologies...
>

I call it 'HVM container' because I use has_hvm_container_domain(d)
| #define has_hvm_container_domain(d) ((d)->guest_type != guest_type_pv)
to check whether TSC scaling can be used by a domain, which, in current
implementation, is either a HVM domain (d->guest_type == guest_type_hvm)
or a PVH domain (d->guest_type == guest_type_pvh).

And I also noticed another macro is_hvm_domain(d)
| #define is_hvm_domain(d) ((d)->guest_type == guest_type_hvm)
so I think 'HVM domain' can not be used to refer to both HVM and PVH
domains.

> Second, even when 'HVM container' can be used as you explained,
> it's inconsistent with other places in same doc, where only 'HVM
> domain' is used. I'd think consistency is more important in this
> patch series, and then if 'HVM container' is really preferred which
> should be a separate patch to update all related docs.
>

Or, maybe I should make it explicit, i.e. using 'HVM and PVH domains'
rather than 'HVM container'.

Haozhong

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