x86/hyperv: Mark the Hyper-V TSC as unstable

The Hyper-V top-level functional specification states, that
"algorithms should be resilient to sudden jumps forward or
backward in the TSC value", this means that we should consider
TSC as unstable. In some cases tsc tests are able to detect the
instability, it was detected in 543 out of 646 boots in my
testing:

 Measured 6277 cycles TSC warp between CPUs, turning off TSC clock.
 tsc: Marking TSC unstable due to check_tsc_sync_source failed

This is, however, just a heuristic. On Hyper-V platform there
are two good clocksources: MSR-based hyperv_clocksource and
recently introduced TSC page.

Signed-off-by: Vitaly Kuznetsov <[email protected]>
Cc: Haiyang Zhang <[email protected]>
Cc: K. Y. Srinivasan <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions