[PATCH v4 05/10] KVM: x86: switch to masterclock update using timekeeper functionality

Denis Plotnikov
2017-08-02T14:39:32Z

It is reasonable to switch KVM to using a more simple, effective
and conceptually correct scheme of dealing with the data needed
for kvm masterclock values calculation.

With the current scheme the kvm needs to have an up-to-date copy of
some timekeeper data to provide a guest using kvmclock with necessary
information.

This is not:
- simple
KVM has to have a lot of code to do that, instead KVM could use
a timekeeper function to get all the data it needs
- effective
the copy of the data used for time data calculation is updated
every time it changed although this is not necessary since
the updated piece of time data is needed in certain moments only
(e.g masterclock updating), instead KVM can request this data
directly form the timekeeper at the moments when it's really needed
- conceptually correct
to do the work (calculate the time data) which the other part
of the system (timekeeper) has been designed and is able to do
is not the proper way, instead deligate the work to the proper part

This patch switches KVM to using the improved timekeeper function for
the kvm masterclock time data.

Removing the leftovers of the old scheme is the matter of the next patches.

Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
---
arch/x86/kvm/x86.c | 26 ++++++++++++++++++--------
1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6c97c82..d8ec2ca 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1643,22 +1643,32 @@ static int do_realtime(struct timespec *ts, u64 *cycle_now)
/* returns true if host is using tsc clocksource */
static bool kvm_get_time_and_clockread(s64 *kernel_ns, u64 *cycle_now)
{
- /* checked again under seqlock below */
- if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
- return false;
+ struct system_time_snapshot systime_snapshot;
+
+ ktime_get_snapshot(&systime_snapshot);
+
+ if (systime_snapshot.cycles_valid) {
+ *kernel_ns = ktime_to_ns(systime_snapshot.boot);
+ *cycle_now = systime_snapshot.cycles;
+ }

- return do_monotonic_boot(kernel_ns, cycle_now) == VCLOCK_TSC;
+ return systime_snapshot.cycles_valid;
}

/* returns true if host is using tsc clocksource */
static bool kvm_get_walltime_and_clockread(struct timespec *ts,
u64 *cycle_now)
{
- /* checked again under seqlock below */
- if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC)
- return false;
+ struct system_time_snapshot systime_snapshot;
+
+ ktime_get_snapshot(&systime_snapshot);
+
+ if (systime_snapshot.cycles_valid) {
+ *ts = ktime_to_timespec(systime_snapshot.real);
+ *cycle_now = systime_snapshot.cycles;
+ }

- return do_realtime(ts, cycle_now) == VCLOCK_TSC;
+ return systime_snapshot.cycles_valid;
}
#endif

--
2.7.4