Marcelo Tosatti <mtosatti@xxxxxxxxxx> wrote:
> Check for KVM_CAP_ADJUST_CLOCK capability KVM_CLOCK_TSC_STABLE, which
> indicates that KVM_GET_CLOCK returns a value as seen by the guest at
> that moment.
>
> For new machine types, use this value rather than reading
> from guest memory.
>
> This reduces kvmclock difference on migration from 5s to 0.1s
> (when max_downtime == 5s).
>
> Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Acked-by: Juan Quintela <quintela@xxxxxxxxxx>
But, if you have to respin it ....
> + /* whether machine supports reliable KVM_GET_CLOCK */
> + bool mach_use_reliable_get_clock;
> +
> + /* whether source host supported reliable KVM_GET_CLOCK */
> + bool src_use_reliable_get_clock;
This two names are really long, but I don't have better suggesitons :-()
> if (running) {
> struct kvm_clock_data data = {};
> - uint64_t time_at_migration = kvmclock_current_nsec(s);
> + uint64_t time_at_migration = 0;
This was not "time_at_migration", it was not already before, but just
now it looks really weird. (as it was already faulty, this is why it is
only a suggestion.)
>
> - s->clock_valid = false;
> + /* local (running VM) restore */
> + if (s->clock_valid) {
> + /*
> + * if host does not support reliable KVM_GET_CLOCK,
> + * read kvmclock value from memory
> + */
> + if (!kvm_has_adjust_clock_stable()) {
> + time_at_migration = kvmclock_current_nsec(s);
> + }
> + /* migration/savevm/init restore */
> + } else {
> + /*
> + * use s->clock in case machine uses reliable
> + * get clock and host where vm was executing
> + * supported reliable get clock
> + */
This comment is just weird. Simplifying
/* If A and B do C */
if (!A and || !B) {
then D();
}
Doing the opposite comment?
Migration code looks rigth.
Once said that, I continue hating clocks.
Later, Juan.
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