src/patches/linux-hyperv_Mark_the_Hyoer-V_TSC_as_unstable.patch

   1 From 88c9281a9fba67636ab26c1fd6afbc78a632374f Mon Sep 17 00:00:00 2001
   2 From: Vitaly Kuznetsov <vkuznets@redhat.com>
   3 Date: Wed, 19 Aug 2015 09:54:24 -0700
   4 Subject: x86/hyperv: Mark the Hyper-V TSC as unstable
   5
   6 The Hyper-V top-level functional specification states, that
   7 "algorithms should be resilient to sudden jumps forward or
   8 backward in the TSC value", this means that we should consider
   9 TSC as unstable. In some cases tsc tests are able to detect the
  10 instability, it was detected in 543 out of 646 boots in my
  11 testing:
  12
  13  Measured 6277 cycles TSC warp between CPUs, turning off TSC clock.
  14  tsc: Marking TSC unstable due to check_tsc_sync_source failed
  15
  16 This is, however, just a heuristic. On Hyper-V platform there
  17 are two good clocksources: MSR-based hyperv_clocksource and
  18 recently introduced TSC page.
  19
  20 Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
  21 Cc: Haiyang Zhang <haiyangz@microsoft.com>
  22 Cc: K. Y. Srinivasan <kys@microsoft.com>
  23 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  24 Cc: Peter Zijlstra <peterz@infradead.org>
  25 Cc: Thomas Gleixner <tglx@linutronix.de>
  26 Cc: devel@linuxdriverproject.org
  27 Link: http://lkml.kernel.org/r/1440003264-9949-1-git-send-email-vkuznets@redhat.com
  28 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  29 ---
  30  arch/x86/kernel/cpu/mshyperv.c | 1 +
  31  1 file changed, 1 insertion(+)
  32
  33 diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
  34 index aad4bd8..6fd023d 100644
  35 --- a/arch/x86/kernel/cpu/mshyperv.c
  36 +++ b/arch/x86/kernel/cpu/mshyperv.c
  37 @@ -141,6 +141,7 @@ static void __init ms_hyperv_init_platform(void)
  38         no_timer_check = 1;
  39  #endif
  40
  41 +       mark_tsc_unstable("running on Hyper-V");
  42  }
  43
  44  const __refconst struct hypervisor_x86 x86_hyper_ms_hyperv = {
  45 --
  46 cgit v0.12
  47