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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.04.12 at 12:37, David Vrabel <dvrabel@xxxxxxxxxx> wrote:
> 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.

Yeah, except that I'm not sure you really need to clear the feature
flags. Just making sure sched_clock_stable never gets set should be
enough; playing with the feature flags always implies that users will
see bigger differences in /proc/cpuinfo between native and Xen
kernels...

Jjan

> 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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