Re: [Xen-devel] Re: [PATCH] clocksource=tsc

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 18/7/08 17:51, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

> I guess you are correct as long as "generate a time record"
> doesn't include recomputing the scaling factor every
> second (which is I think what introduces the jitter... see
> more on this below).
> 
> However, I'm not sure why you perceive the aesthetics to
> be so bad to put "if (ideal_clocksource)" in get_s_time()
> and a few other places in time.c... or for that matter in
> the PV guest code.

Extra special case are ugly. And then if they extend into the guests then
you also have to worry about new guests on old Xen and old guests on new Xen
(i.e., compatibility both ways). Which is not a good way to go when there is
an easy way to hide this new implementation from guests. Indeed we would
only update the TSC and system-time stamps -- the scale factor would never
change.

 -- Keir



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