lantianyu1986@gmail.com writes:
From: Tianyu Lan <redacted>
Hyper-V guests use the default native_sched_clock() in pv_ops.time.sched_clock
on x86. But native_sched_clock() directly uses the raw TSC value, which
can be discontinuous in a Hyper-V VM. Add the generic hv_setup_sched_clock()
to set the sched clock function appropriately. On x86, this sets
pv_ops.time.sched_clock to read the Hyper-V reference TSC value that is
scaled and adjusted to be continuous.
Hypervisor can, in theory, disable TSC page and then we're forced to use
MSR-based clocksource but using it as sched_clock() can be very slow,
I'm afraid.
On the other hand, what we have now is probably worse: TSC can,
actually, jump backwards (e.g. on migration) and we're breaking the
requirements for sched_clock().
--
Vitaly