Re: [PATCH] x86/Hyper-V: Fix hv sched clock function return wrong time unit

[Tianyu Lan]

Hi Vitaly:
    Thanks for your review.

On 3/24/2020 11:49 PM, Vitaly Kuznetsov wrote:
> Yubo Xie <ltykernel@xxxxxxxxx> writes:
>
> > sched clock callback should return time with nano second as unit
> > but current hv callback returns time with 100ns. Fix it.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Yubo Xie <yuboxie@xxxxxxxxxxxxx>
> > Signed-off-by: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
> > Fixes: adb87ff4f96c ("clocksource/drivers/hyperv: Allocate Hyper-V TSC page statically")
>
> I don't think this is the right commit to reference,
>
> commit bd00cd52d5be655a2f217e2ed74b91a71cb2b14f
> Author: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
> Date:   Wed Aug 14 20:32:16 2019 +0800
>
>      clocksource/drivers/hyperv: Add Hyper-V specific sched clock function
>
> looks like the one.

Sorry. You are right. Will update in the next version.

> > ---
> >   drivers/clocksource/hyperv_timer.c | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
> > index 9d808d595ca8..662ed978fa24 100644
> > --- a/drivers/clocksource/hyperv_timer.c
> > +++ b/drivers/clocksource/hyperv_timer.c
> > @@ -343,7 +343,8 @@ static u64 notrace read_hv_clock_tsc_cs(struct clocksource *arg)
> >   
> >   static u64 read_hv_sched_clock_tsc(void)
> >   {
> > -	return read_hv_clock_tsc() - hv_sched_clock_offset;
> > +	return (read_hv_clock_tsc() - hv_sched_clock_offset)
> > +		* (NSEC_PER_SEC / HV_CLOCK_HZ);
> >   }
> >   
> >   static void suspend_hv_clock_tsc(struct clocksource *arg)
> > @@ -398,7 +399,8 @@ static u64 notrace read_hv_clock_msr_cs(struct clocksource *arg)
> >   
> >   static u64 read_hv_sched_clock_msr(void)
> >   {
> > -	return read_hv_clock_msr() - hv_sched_clock_offset;
> > +	return (read_hv_clock_msr() - hv_sched_clock_offset)
> > +		* (NSEC_PER_SEC / HV_CLOCK_HZ);
> >   }
>
> kvmclock seems to have the same (pre-patch) code ...


kvm sched clock gets time from pvclock_clocksource_read() and
the time unit is nanosecond. So there is such issue in KVM code.

> >   
> >   static struct clocksource hyperv_cs_msr = {