open-vm-tools-devel

Hooks in time synchronization

[Christian G. <chr...@go...>]

Hi all,

I'm currently running several virtual machines on VMware ESXI 4.1 and am
wondering whether there is a possibility to explicitely steer the system
time (wall clock) of selected virtual machines instead of letting them
synchronize to VMware ESXI base system time.

So: are there hooks in the time synchronization module (vmsync ?) to dictate
a VM's wall clock such that dependent on the external time dictate module
the selected wall clock inside the VM runs faster or slower than (in general
asynchronous to) the base system time?

Why: want to run accelerated or slown down network emulations similiar to a
project called slicetime:
http://www.comsys.rwth-aachen.de/research/projects/slicetime/

Any help or hints are highly appreciated!

Thanks & Best regards,

Chris.

Re: Hooks in time synchronization

[Dmitry T. <dt...@vm...>]

Hi Christian,

On Tuesday, May 10, 2011 04:25:10 AM Christian Glomb wrote:
> Hi all,
> 
> I'm currently running several virtual machines on VMware ESXI 4.1 and am
> wondering whether there is a possibility to explicitely steer the system
> time (wall clock) of selected virtual machines instead of letting them
> synchronize to VMware ESXI base system time.
> 
> So: are there hooks in the time synchronization module (vmsync ?) to
> dictate a VM's wall clock such that dependent on the external time
> dictate module the selected wall clock inside the VM runs faster or
> slower than (in general asynchronous to) the base system time?
> 
> Why: want to run accelerated or slown down network emulations similiar
> to a project called slicetime:
> http://www.comsys.rwth-aachen.de/research/projects/slicetime/

There are no such hooks in the timesync plug in, however you should be able 
to disable the standard time synchronization in guest (vmware-toolbox-cmd 
timesync disable) and then drive it yourself.

Hope this helps,

Dmitry

Re: Hooks in time synchronization

[Christian G. <chr...@go...>]

Hi Dmitry,

thanks for your reply! Any idea how to drive system time?

An idea might be to redirect standard time sync for a certain VM to a custom
kernel module (running on the ESXI base system) being steered from outside,
i.e.:

External control <-> Kernel module on ESXI <-> time sync (vmware tools)
inside VM

In XEN this can be done via the hypercall functions. Are there any related
functions in VMware?

Thanks,

Chris.

Re: Hooks in time synchronization

[Dmitry T. <dt...@vm...>]

Hi Christian,

On Monday, May 23, 2011 06:55:20 AM Christian Glomb wrote:
> Hi Dmitry,
> 
> thanks for your reply! Any idea how to drive system time?
> 
> An idea might be to redirect standard time sync for a certain VM to a
> custom kernel module (running on the ESXI base system) being steered
> from outside, i.e.:
> 
> External control <-> Kernel module on ESXI <-> time sync (vmware tools)
> inside VM
> 
> In XEN this can be done via the hypercall functions. Are there any
> related functions in VMware?

No, there is not, but if you take a look at the sources of timeSync plugin 
you will see how you can slow down and speed up guest time using 
adjtime()/adjtimex(). Or you could have guests sync up with a custom 
version of NTP server that you deploy somewhere on your network.

Thanks,
Dmitry