Re: [Xen-devel] Debian stable kernel got timer issue when running as PV guest

[David Vrabel <dvrabel@xxxxxxxxxx>]

On 13/04/12 08:56, Jan Beulich wrote:
>>>> On 12.04.12 at 21:22, Sheng Yang <sheng@xxxxxxxxxx> wrote:
>> I've compiled a kernel, force sched_clock_stable=0, then it solved the
>> timestamp jump issue as expected. Luckily, seems it also solved the call
>> trace and guest hang issue as well.
> 
> And this is also how it should be fixed.

Something like this?  I've not tested it yet as I need to track down
some of the problem hardware and get it set up.

8<---------------
xen: always set the sched clock as unstable

It's not clear to me if the Xen clock source can be used as a stable
sched clock. Also, even if the guest is started on a system whose
underying TSC is stable it may be migrated to one where it's not. So
never mark the sched clock as stable.

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
 arch/x86/xen/time.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 0296a95..b22cd9c 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -473,6 +473,9 @@ static void __init xen_time_init(void)
        do_settimeofday(&tp);

        setup_force_cpu_cap(X86_FEATURE_TSC);
+       setup_clear_cpu_cap(X86_FEATURE_CONSTANT_TSC);
+       setup_clear_cpu_cap(X86_FEATURE_NONSTOP_TSC);
+       sched_clock_stable = 0;

        xen_setup_runstate_info(cpu);
        xen_setup_timer(cpu);

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