On Wednesday, 10/11/2006 at 07:58 CST, Paul Gilmartin <[EMAIL PROTECTED]> wrote:
> The same Redpiece warns against guests' attempting to set the > TOD clock (presumably with SCK). And it mentions a "software" > clock which is initialized from the TOD clock at startup. And > I'm at a loss to understand how a clock could be implemented > entirely in software and be immune to any irregularities in > some underlying hardware clock. There is no software clock. The Interpretive Execution Facility (SIE) understands the concept of "virtual time". It applies deltas to the real TOD to obtain the virtual TOD. A virtual TOD drifts at the same rate as the real TOD. And I say "real TOD" when I actually mean "logical TOD". When the partition does a Set Clock, a partition-level delta is again applied via SIE. (The Interpretive Execution Facility provides the mechanism by which both LPARs and virtual machines are created.) But I think even Linux does not Set Clock, but instead itself applies a [learned via NTP, e.g.] delta to the TOD to obtain "system" time. Alan Altmark z/VM Development IBM Endicott ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
