This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


Re: [Xen-devel] HPET/PIT timer accuracy

On 29 Jul 2005, at 19:17, Michael Hohnbaum wrote:

The TSC is not a reliable time source.  There is no guarantee of
synchronization between multiple CPUs.  Also note that the TSC will
stop in ACPI C3 mode.  Probably not an issue for Xen today, but could
be in the future, especially as servers start doing more power
management.  The HPET is preferable for a time source on systems
that this is available on.

We're not relying on TSC synchronisation between CPUs. They can run at different frequencies, stop in deep sleep, and so on. But we *do* want the frequency of each one to be as stable as possible. I'd expect to get <1ppm stability from a crystal source at constant temperature, no problem.

 -- Keir

Xen-devel mailing list