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 21:57:52 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.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

Hi Vitaly:
     Thanks for your review.

On 3/24/2020 11:49 PM, Vitaly Kuznetsov wrote:
> Yubo Xie <ltykernel@...il.com> writes:
> 
>> sched clock callback should return time with nano second as unit
>> but current hv callback returns time with 100ns. Fix it.
>>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Yubo Xie <yuboxie@...rosoft.com>
>> Signed-off-by: Tianyu Lan <Tianyu.Lan@...rosoft.com>
>> 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@...rosoft.com>
> 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 = {
>