Re: [Xen-devel] [RFC] Physical hot-add cpus and TSC

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 28/05/2010 15:35, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

>> "Undetectable" by Dan's definition means undetectable by
>> a multi-threaded app on a multi-vcpu guest. Any detected
>> warp would therefore be a problem.
> 
> This is actually Linux's definition, a requirement
> for selecting tsc as Linux's default clocksource,
> and measured by the same algorithm in Xen and Linux.

Well, to be precise, it's Linux's definition for whether TSC is a suitable
basis for the kernel's monotonic clock source. Linux doesn't make strong
guarantees to applications about TSC semantics, by synthesising TSC, or
anything like that. Applying the same constraints on the TSC all the way up
to application level was your own proposal.

Anyhow, retreading this argument is not going to be fruitful. It's fair to
say that your definition is now also Xen's definition.

 -- Keir



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