Messages in this thread | | | From | Michael Kelley <> | Subject | RE: [PATCH] Hyper-V: fix for unwanted manipulation of sched_clock when TSC marked unstable | Date | Tue, 13 Jul 2021 17:25:59 +0000 |
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From: Ani Sinha <ani@anisinha.ca> Sent: Monday, July 12, 2021 8:05 PM > > Marking TSC as unstable has a side effect of marking sched_clock as > unstable when TSC is still being used as the sched_clock. This is not > desirable. Hyper-V ultimately uses a paravirtualized clock source that > provides a stable scheduler clock even on systems without TscInvariant > CPU capability. Hence, mark_tsc_unstable() call should be called _after_ > scheduler clock has been changed to the paravirtualized clocksource. This > will prevent any unwanted manipulation of the sched_clock. Only TSC will > be correctly marked as unstable. > > Signed-off-by: Ani Sinha <ani@anisinha.ca> > --- > arch/x86/kernel/cpu/mshyperv.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c > index 22f13343b5da..715458b7729a 100644 > --- a/arch/x86/kernel/cpu/mshyperv.c > +++ b/arch/x86/kernel/cpu/mshyperv.c > @@ -370,8 +370,6 @@ static void __init ms_hyperv_init_platform(void) > if (ms_hyperv.features & HV_ACCESS_TSC_INVARIANT) { > wrmsrl(HV_X64_MSR_TSC_INVARIANT_CONTROL, 0x1); > setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE); > - } else { > - mark_tsc_unstable("running on Hyper-V"); > } > > /* > @@ -432,6 +430,12 @@ static void __init ms_hyperv_init_platform(void) > /* Register Hyper-V specific clocksource */ > hv_init_clocksource(); > #endif > + /* TSC should be marked as unstable only after Hyper-V > + * clocksource has been initialized. This ensures that the > + * stability of the sched_clock is not altered. > + */
For multi-line comments like the above, the first comment line should just be "/*". So:
/* * TSC should be marked as unstable only after Hyper-V * clocksource has been initialized. This ensures that the * stability of the sched_clock is not altered. */
> + if (!(ms_hyperv.features & HV_ACCESS_TSC_INVARIANT)) > + mark_tsc_unstable("running on Hyper-V"); > } > > static bool __init ms_hyperv_x2apic_available(void) > -- > 2.25.1
Modulo the comment format,
Reviewed-by: Michael Kelley <mikelley@microsoft.com> Tested-by: Michael Kelley <mikelley@microsoft.com>
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