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 <vkuznets@redhat.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: devel@linuxdriverproject.org
Link: http://lkml.kernel.org/r/1440003264-9949-1-git-send-email-vkuznets@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Vitaly Kuznetsov 2015-08-19 09:54:24 -07:00 committed by Ingo Molnar
parent 955381dd65
commit 88c9281a9f
1 changed files with 1 additions and 0 deletions

View File

@ -141,6 +141,7 @@ static void __init ms_hyperv_init_platform(void)
no_timer_check = 1;
#endif
mark_tsc_unstable("running on Hyper-V");
}
const __refconst struct hypervisor_x86 x86_hyper_ms_hyperv = {