Hi Folks, Still seeking your guidance on this. Appreciate any pointers you may have.
Thanks much. -a On Fri, Sep 9, 2011 at 11:28 AM, al pat <alps....@gmail.com> wrote: > > We are doing an experiment with kvm-clock to validate its effectiveness, > particularly when running NTP on the host to make sure the host’s clock > stays properly sync. > Our observations leads us to a few unanswered questions, including the > possibility of a bug (our our misunderstanding of how kvm_clock should > work). > > Our understanding is that kvm_clock will help sync the clock between the > host and the guest. We do not observe this to happen in reality and thus > this question. > > We are using Ubuntu 11.04 on the host and the guest. > > The command we issue to launch the VM is the following: > > $ sudo kvm -m 500 -rtc clock=host guestos.img > > We also arranged for Ubuntu to show the seconds on the clock displayed in > the menu. > > Observation 1: > Upon launching the VM, we see a time difference between the 2 clock ranging > from 1 to 2 seconds. > > Observation 2: > If we change the date on the host (with a command such as “date --set > 10:00:00 AM Sep 9, 2011”), the time on the guest remains the same, > unaffected. > > Observation 3: > After running for a while without NTP on the host, we run “ntpdate” to sync > up the host, but the guest stick with whatever previous time. > > > Another test we will run is to have ntpd on the host and wait for an > extended time to see if the guest drifts away from that original 1 or 2 > second lag. In the meantime, we are asking you for some input in this > regards: > Questions > -What does the “–rtc clock” option is supposed to mean exactly? According > to the man page, the guest should get its time from the host, but neither > date nor an “ntpdate” affected the clock on the guest. > -What are the other options that we should use? > > -rtc [base=utc|localtime|date][,clock=host|vm][,driftfix=none|slew] > Specify base as "utc" or "localtime" to let the RTC start at the > current UTC or local time, respectively. "localtime" is required > for correct date in MS-DOS or Windows. To start at a specific > point > in time, provide date in the format "2006-06-17T16:01:21" or > "2006-06-17". The default base is UTC. > > By default the RTC is driven by the host system time. This allows > to use the RTC as accurate reference clock inside the guest, > specifically if the host time is smoothly following an accurate > external reference clock, e.g. via NTP. If you want to isolate > the > guest time from the host, even prevent it from progressing during > suspension, you can set clock to "vm" instead. > > Enable driftfix (i386 targets only) if you experience time drift > problems, specifically with Windows' ACPI HAL. This option will > try > to figure out how many timer interrupts were not processed by the > Windows guest and will re-inject them. > > > Can someone shed light on what we are missing? Any pointers will be > helpful. > > Thanks > -a > >
