Timekeeping in stable/9

[Martin Sugioarto]

Am Wed, 18 Jan 2012 07:50:49 +0100
schrieb Martin Sugioarto <martin at sugioarto.com>:

> I can confirm this on VirtualBox. I've been running WinXP inside
> VirtualBox and measured network I/O during downloads. It showed me
> very high download rates (around 800kB/s) while it's physically
> possible to download 200kB/s through DSL here (Germany sucks with
> DSL, even in largest cities, btw!).
> 
> I correlated this behavior with high disk I/O on the host. That means
> that the timer issues on the virtual host appear when I start a
> larger cp job on the host. I also immediately thought that this has
> something to do with timers.

Hi everybody,

I just want to add some information on this. I tested a few things with
VirtualBox yesterday.

I switched off ntpd on the host and tested if there are differences,
but the clock is working correctly on the host. I tested it a few times,
it is stable, as I expect it to be.

It seems to be rather a software problem with VirtualBox. I can see that
when the host is under heavy load (CPU!) the guest does not get enough
runtime to adjust the clock correctly. After a few minutes there has
been a difference of 50 seconds between the host and guest clock. And
furthermore, I don't quite understand how the real time clock works in
VirtualBox but it seems to slide in the different directions causing
weird results with progress bars on MS-Windows XP.

I just want to explain why I thought that I/O influences this. I have
got my hard disk encrypted, so it puts some load on the CPU, too.

If you want to test VirtualBox behavior, you can simple dd
from /dev/random and look at the weird results in VirtualBox.

--
I hope it helps further,
Martin
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