wallclock time for paravirtualized guests

wallclock time for paravirtualized guests

[Bruce Rogers]

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The paravirtualized guests are offered wallclock time referenced to UTC
only, while fully virtualized guests are given the option via the config
file (localtime parameter) of starting with UTC time or local time.
What would it take to optionally provide localtime to the
paravirtualized guests as well?
For a guest that launches assuming localtime as its time basis, then
later deriving UTC from it based on configuration files, this is
problematic, requiring some convolutions to how it handles time as it
boots.
Is there some place where we can insert a localtime offset into the
start-of-day structure, or perhaps change the sharedinfo wallclock time
to be either localtime or utc, depending on a localtime parameter in the
config file, similar to what is done for fully virtualized guests?
 
- Bruce Rogers

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RE: wallclock time for paravirtualized guests

[Ian Pratt]

> The paravirtualized guests are offered wallclock time 
> referenced to UTC only, while fully virtualized guests are 
> given the option via the config file (localtime parameter) of 
> starting with UTC time or local time.
> What would it take to optionally provide localtime to the 
> paravirtualized guests as well?
> For a guest that launches assuming localtime as its time 
> basis, then later deriving UTC from it based on configuration 
> files, this is problematic, requiring some convolutions to 
> how it handles time as it boots.
> Is there some place where we can insert a localtime offset 
> into the start-of-day structure, or perhaps change the 
> sharedinfo wallclock time to be either localtime or utc, 
> depending on a localtime parameter in the config file, 
> similar to what is done for fully virtualized guests?

I guess it might be useful to be able to configure a 'wallclock offset
in seconds' for a domain. It would need to be implemented in Xen and set
via a dom0 op.

Ian 

RE: wallclock time for paravirtualized guests

[Bruce Rogers]

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I'll see about putting together a patch then.
Is it OK to simply have wc_sec altered by an optional, per domain time
offset from UTC in seconds (hence binary no change to the interface), or
do you think there should be another field provided that is the offset,
leaving wc_sec unmodified?
 
- Bruce Rogers

>>> "Ian Pratt" <m+Ian.Pratt@cl.cam.ac.uk> 3/27/2006 8:40:16 pm >>>
> The paravirtualized guests are offered wallclock time 
> referenced to UTC only, while fully virtualized guests are 
> given the option via the config file (localtime parameter) of 
> starting with UTC time or local time.
> What would it take to optionally provide localtime to the 
> paravirtualized guests as well?
> For a guest that launches assuming localtime as its time 
> basis, then later deriving UTC from it based on configuration 
> files, this is problematic, requiring some convolutions to 
> how it handles time as it boots.
> Is there some place where we can insert a localtime offset 
> into the start-of-day structure, or perhaps change the 
> sharedinfo wallclock time to be either localtime or utc, 
> depending on a localtime parameter in the config file, 
> similar to what is done for fully virtualized guests?

I guess it might be useful to be able to configure a 'wallclock offset
in seconds' for a domain. It would need to be implemented in Xen and
set
via a dom0 op.

Ian 

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Re: wallclock time for paravirtualized guests

[Keir Fraser]

On 28 Mar 2006, at 16:28, Bruce Rogers wrote:

> I'll see about putting together a patch then.
> Is it OK to simply have wc_sec altered by an optional, per domain time 
> offset from UTC in seconds (hence binary no change to the interface), 
> or do you think there should be another field provided that is the 
> offset, leaving wc_sec unmodified?

The former. No need to change the guest ABI.

  -- Keir

wallclock time for paravirtualized guests

[Bruce Rogers]

The paravirtualized guests are offered wallclock time referenced to UTC only, while fully virtualized guests are given the option via the config file (localtime parameter) of starting with UTC time or local time.
What would it take to optionally provide localtime to the paravirtualized guests as well?
For a guest that launches assuming localtime as its time basis, then later deriving UTC from it based on configuration files, this is problematic, requiring some convolutions to how it handles time as it boots.
Is there some place where we can insert a localtime offset into the start-of-day structure, or perhaps change the sharedinfo wallclock time to be either localtime or utc, depending on a localtime parameter in the config file, similar to what is done for fully virtualized guests?
 
- Bruce Rogers