Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1209956

[PATCH] hyper-v: mark TSC as unstable

Show all headers | View raw

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>
---
 arch/x86/kernel/cpu/mshyperv.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index aad4bd8..6fd023d 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -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 = {
-- 
2.4.3

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

[PATCH] hyper-v: mark TSC as unstable Vitaly Kuznetsov <vkuznets@redhat.com> - 2015-08-19 19:00 +0200
  [tip:x86/platform] x86/hyperv: Mark the Hyper-V TSC as unstable tip-bot for Vitaly Kuznetsov <tipbot@zytor.com> - 2015-08-21 09:50 +0200
    Re: [tip:x86/platform] x86/hyperv: Mark the Hyper-V TSC as unstable Peter Zijlstra <peterz@infradead.org> - 2015-08-21 16:40 +0200
      RE: [tip:x86/platform] x86/hyperv: Mark the Hyper-V TSC as unstable KY Srinivasan <kys@microsoft.com> - 2015-08-21 17:40 +0200

csiph-web