[Xen-devel] Re: [PATCH] strictly increasing hvm guest time

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 2/7/08 17:03, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

> This simple one-line patch changes hvm guest time from
> monotonically non-decreasing to monotonically strictly-
> increasing.  As a result, two consecutive reads of the
> (virtual) hpet will never return the same value, thus
> avoiding the appearance that time has stopped (which may
> occur if there is skew between physical processor TSCs).

It does seem a little hack-ish, if we don't know of any issues arising from
the current code, and we expect cross-cpu deltas to be pretty small. Also
guests will often convert HPET reads to well-known units (e.g.,
microseconds, milliseconds) before using them, in which case even a delta of
one may not result in differing converted time values.

 -- Keir



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