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

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Date:   Wed, 25 Mar 2020 15:28:45 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Tianyu Lan <ltykernel@...il.com>
Cc:     Yubo Xie <yuboxie@...rosoft.com>, linux-hyperv@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>, kys@...rosoft.com,
        haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        liuwe@...rosoft.com, daniel.lezcano@...aro.org, tglx@...utronix.de,
        michael.h.kelley@...rosoft.com
Subject: Re: [PATCH] x86/Hyper-V: Fix hv sched clock function return wrong time unit

Tianyu Lan <ltykernel@...il.com> writes:

>>> @@ -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.
>

Ah, true, kvmclock is always 1Ghz so it's reading 'naturally' converts
to ns.

-- 
Vitaly