On Tue, Jul 13, 2021 at 01:04:46PM +0000, Wei Liu wrote: > On Tue, Jul 13, 2021 at 08:35:21AM +0530, Ani Sinha wrote: > > Marking TSC as unstable has a side effect of marking sched_clock as > > unstable when TSC is still being used as the sched_clock. This is not > > desirable. Hyper-V ultimately uses a paravirtualized clock source that > > provides a stable scheduler clock even on systems without TscInvariant > > CPU capability. Hence, mark_tsc_unstable() call should be called _after_ > > scheduler clock has been changed to the paravirtualized clocksource. This > > will prevent any unwanted manipulation of the sched_clock. Only TSC will > > be correctly marked as unstable. > > Correct me if I'm wrong, what you're trying to address is that > sched_clock remains marked as unstable even after Linux has switched to > a stable clock source. > > I think a better approach will be to mark the sched_clock as stable when > we switch to the paravirtualized clock source. No.. unstable->stable transitions are unsound. You get to switch to your paravirt clock earlier.
