From mboxrd@z Thu Jan 1 00:00:00 1970 From: Priya Subject: Re: Xen timing mode Date: Tue, 23 Feb 2010 12:12:07 -0500 Message-ID: <5c3550fe1002230912j1a5d0650oa1e355652c8e3062@mail.gmail.com> References: <27706447.post@talk.nabble.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============1552930172==" Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser Cc: "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org --===============1552930172== Content-Type: multipart/alternative; boundary=00504502aeeb4a4515048047a626 --00504502aeeb4a4515048047a626 Content-Type: text/plain; charset=ISO-8859-1 Thanks ! In that case, how does a para-virtualized user domain find the domain - virtual time ? --Priya On Tue, Feb 23, 2010 at 12:08 PM, Keir Fraser wrote: > Independent_wallclock is specific to Linux PV guests, and is set within the > guest. Timer_mode is specific to HVM guests and is a domain build-time > config option. > > -- Keir > > On 23/02/2010 16:50, "PBhat" wrote: > > > > > A question about timing modes in Xen came up after reading the > documentation > > on > > > http://wiki.xensource.com/xenwiki/XenConfigurationFileOptions?highlight=(inter > > rupts)|(timer) > > configuration file options and I was wondering if you could help me with > > it. > > > > * I know that Xen has a facility on the user domains to change the > > timing from something called the ' > http://openskill.info/infobox.php?ID=1451 > > independent wallclock ' to 'dependent clock' and vice versa. The way to > do > > this is to toggle the parameter /proc/sys/xen/independent_wallclock > between > > 0 (dependent) and 1 (independent) > > > > > > * Now, the documentation on the configuration options for xen virtual > > machine under the heading of Timers contains no mention of the above > > mentioned facility, but instead talks about something called a > 'timer_mode' > > > > > > timer_mode: Timer mode (0=delay virtual time when ticks are missed; > > 1=virtual time is always wallclock time > > timer_mode (default=1; Value='TIMER_MODE') > > > > Now my question is whether the timer mode = 1 is equivalent to > independent_ > > wallclock? > > > > I think the answer is no. While timer_mode = 1 decides whether the > virtual > > machine is able to read the Domain-0 time, the independent_wallclock > decides > > whether you need NTP sychronization on both (user and control) domains or > > not. > > > > Namely, in the timer_mode = 1, the gettimeofday() called from the virtual > > machine will return the domain virtual time, but time_mode = 0 > > gettimeofday() instruction from the virtual machine will return the > system > > time. > > > > The independent and dependent modes have an effect on whether the virtual > > machines can use the NTP or any other synchronization of Domain-0. > > > > Is my understanding correct? > > > > I further want to know whether the working remains similar on Xen HVMs > also. > > In the sense that are Hardware based virtual machines capable of reading > the > > Domain-0 system time in an analogous way? > > > > > > Your help would be much appreciated. I am new to this area and I > apologize > > if my questions seem too basic. > > > > --00504502aeeb4a4515048047a626 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Thanks !

In that case, how does a para-virtualized user domain find = the domain - virtual time ?

--Priya

On Tue, Feb 23, 2010 at 12:08 PM, Keir Fraser <keir.fraser@eu.citrix.com><= /span> wrote:
Independent_wallc= lock is specific to Linux PV guests, and is set within the
guest. Timer_mode is specific to HVM guests and is a domain build-time
config option.

=A0-- Keir

On 23/02/2010 16:50, "PBhat" <pbhat@acis.ufl.edu> wrote:

>
> A question about timing modes in Xen came up after reading the documen= tation
> on
> http://wiki.xensource.com/xenwik= i/XenConfigurationFileOptions?highlight=3D(inter
> rupts)|(timer)
> configuration file options =A0and I was wondering if you could help me= with
> it.
>
> =A0 =A0 * I know that Xen has a facility on the user domains to change= the
> timing from something called the ' http://openskill.info/infobox.ph= p?ID=3D1451
> independent wallclock ' to 'dependent clock' and vice vers= a. The way to do
> this is to toggle the parameter /proc/sys/xen/independent_wallclock be= tween
> 0 (dependent) and 1 (independent)
>
>
> =A0 =A0 * Now, the documentation on the configuration options for xen = virtual
> machine under the heading of Timers contains no mention of the above > mentioned facility, but instead talks about something called a 'ti= mer_mode'
>
>
> =A0timer_mode: Timer mode (0=3Ddelay virtual time when ticks are misse= d;
> 1=3Dvirtual time is always wallclock time
> =A0 =A0 =A0 timer_mode (default=3D1; Value=3D'TIMER_MODE')
>
> Now my question is whether the timer mode =A0=3D 1 is equivalent to in= dependent_
> wallclock?
>
> I think the answer is no. While timer_mode =3D 1 decides whether the v= irtual
> machine is able to read the Domain-0 time, the independent_wallclock d= ecides
> whether you need NTP sychronization on both (user and control) domains= or
> not.
>
> Namely, in the timer_mode =3D 1, the gettimeofday() called from the vi= rtual
> machine will return the domain virtual time, but time_mode =3D 0
> gettimeofday() instruction from the virtual machine will return the sy= stem
> time.
>
> The independent and dependent modes have an effect on whether the virt= ual
> machines can use the NTP or any other synchronization of Domain-0.
>
> Is my understanding correct?
>
> I further want to know whether the working remains similar on Xen HVMs= also.
> In the sense that are Hardware based virtual machines capable of readi= ng the
> Domain-0 system time in an analogous way?
>
>
> Your help would be much appreciated. I am new to this area and I apolo= gize
> if my questions seem too basic.




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