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[SRU,t/u/v] x86/hyperv: Mark the Hyper-V TSC as unstable

Message ID 1445455928-480-1-git-send-email-tim.gardner@canonical.com
State New
Headers show

Commit Message

Tim Gardner Oct. 21, 2015, 7:32 p.m. UTC 
From: Vitaly Kuznetsov <vkuznets@redhat.com>

BugLink: http://bugs.launchpad.net/bugs/1498206

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>
(cherry picked from commit 88c9281a9fba67636ab26c1fd6afbc78a632374f)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---
 arch/x86/kernel/cpu/mshyperv.c | 1 +
 1 file changed, 1 insertion(+)

Comments

Stefan Bader Oct. 22, 2015, 8:41 a.m. UTC | #1
Brad Figg Oct. 26, 2015, 8:57 p.m. UTC | #2 
Applied to the master-next and lts-backport-utopic-next branches of Trusty
and the master-next branch of Vivid.
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Patch

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 8915833..8906637 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -103,6 +103,7 @@  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 = {