On 10/17/2009 04:28 AM, Glauber Costa wrote:
When we migrate a kvm guest that uses pvclock between two hosts, we may
suffer a large skew. This is because there can be significant differences
between the monotonic clock of the hosts involved. When a new host with
a much larger monotonic time starts running the guest, the view of time
will be significantly impacted.
Situation is much worse when we do the opposite, and migrate to a host with
a smaller monotonic clock.
This proposed ioctl will allow userspace to inform us what is the monotonic
clock value in the source host, so we can keep the time skew short, and
more importantly, never goes backwards. Userspace may also need to trigger
the current data, since from the first migration onwards, it won't be
reflected by a simple call to clock_gettime() anymore.
+struct kvm_clock_data {
+ __u64 clock;
+ __u64 pad[2];
+};
+
The padding is not reusable without a flags word that we can set bits in
for extended functionality. Please add one (and a check that it is
zero, or -EINVAL).
Since it was already applied, please do it as an incremental patch.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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