Re: [KVM TSC trapping / migration 2/2] Add TSC KHZ MSR

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 01/07/2011 12:48 AM, Marcelo Tosatti wrote:
On Thu, Jan 06, 2011 at 12:10:45AM -1000, Zachary Amsden wrote:
Use an MSR to allow "soft" migration to hosts which do not support
TSC trapping.  Rather than make this a required element of any
migration protocol, we allow the TSC rate to be exported as a data
field (useful in its own right), but we also allow a one time write
of the MSR during VM creation.  The result is that for the common
use case, no protocol change is required to communicate TSC rate
to the receiving host.
Migration to hosts which do not support the feature can be achieved by
saving/restoring the TSC rate + flags in a subsection. A subsection
seems more appropriate than an MSR for this.

Yes, I looked at that, but it looked to me like a subsection was intended for an optional feature which MUST be present on the destination if the source is using the feature. This way, newer hosts without the feature enabled can migrate to older hosts which do not support the feature.

The TSC rate migration is slightly different; we may wish to migrate from a host with the TSC rate feature enabled to a host which does not support the TSC rate feature. This is exactly the current behavior, the TSC rate will change on that migration, and I wanted to preserve that behavior. I don't advise that mode of usage, but there may be use cases for it and it should be decided by policy, not dictated by our feature set.

That said, I'm happy to remove the MSR if we truly don't want to support that mode of usage.

Zach
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux