On 01.08.2017 15:41, Paolo Bonzini wrote:
On 01/08/2017 14:11, Denis Plotnikov wrote:
In fact, this "cycles_valid" is going to be used for deciding whether to
use KVM masterclock or not. And if it's not we still want to know
cycles_stamp value to use it in KVM.
Why? Neither pvclock_update_vm_gtod_copy nor kvm_pv_clock_pairing do
anything with the two variables that are passed by reference, if the
read returns false. Hence my suggestion of calling it cycles_valid.
giving up
So the cycles is valid, but clocksource is not reliable (why? let decide
to a clocksource, by default assume they are all not stable), thus we
must calculate time values for a guest each time its needed.
So, my proposal is to name the variable sightly differently: cs_reliable
and go like:
if (clock->read_clock_with_stamp) {
systime_snapshot->cs_reliable =
clock->read_clock_with_stamp(
&now, &systime_snapshot->cycles);
} else {
now = tk_clock_read(&tk->tkr_mono);
systime_snapshot->cs_reliable = false;
systime_snapshot->cycles = now;
}
What do you think?
I'm afraid you still have to define the meaning of "reliable". (Though
I agree that the right default is false, that was a thinko on my side.
This also means that you need to define read_clock_with_stamp for the
TSC clocksource too).
Paolo
agree
name: cycles_valid
default: false
read_clock_with_stamp: defined for tsc returning true
Thanks!
Patches are in progress.
They well be sent soon, nice and shiny!
Denis
