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From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Tianyu Lan <ltykernel@gmail.com>
Cc:     Yubo Xie <yuboxie@microsoft.com>, linux-hyperv@vger.kernel.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Tianyu Lan <Tianyu.Lan@microsoft.com>, kys@microsoft.com,
        haiyangz@microsoft.com, sthemmin@microsoft.com,
        liuwe@microsoft.com, daniel.lezcano@linaro.org, tglx@linutronix.de,
        michael.h.kelley@microsoft.com
Subject: Re: [PATCH] x86/Hyper-V: Fix hv sched clock function return wrong time unit
In-Reply-To: <039e126f-f00d-d7e1-aa92-c049c9e3333b@gmail.com>
References: <20200324151935.15814-1-yuboxie@microsoft.com> <87ftdx7nxv.fsf@vitty.brq.redhat.com> <039e126f-f00d-d7e1-aa92-c049c9e3333b@gmail.com>
Date:   Wed, 25 Mar 2020 15:28:45 +0100
Message-ID: <87lfno5x0i.fsf@vitty.brq.redhat.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
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Tianyu Lan <ltykernel@gmail.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