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

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

[Yubo Xie]

sched clock callback should return time with nano second as unit
but current hv callback returns time with 100ns. Fix it.

Cc: stable@vger.kernel.org
Signed-off-by: Yubo Xie <yuboxie@microsoft.com>
Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
Fixes: adb87ff4f96c ("clocksource/drivers/hyperv: Allocate Hyper-V TSC page statically")
---
 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);
 }
 
 static struct clocksource hyperv_cs_msr = {
-- 
2.14.5

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

[Vitaly Kuznetsov]

Yubo Xie <ltykernel@gmail.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@vger.kernel.org
> Signed-off-by: Yubo Xie <yuboxie@microsoft.com>
> Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.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@microsoft.com>
Date:   Wed Aug 14 20:32:16 2019 +0800

    clocksource/drivers/hyperv: Add Hyper-V specific sched clock function

looks like the one.

> ---
>  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 ...

>  
>  static struct clocksource hyperv_cs_msr = {

-- 
Vitaly

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

[Sasha Levin]

Hi

[This is an automated email]

This commit has been processed because it contains a "Fixes:" tag
fixing commit: adb87ff4f96c ("clocksource/drivers/hyperv: Allocate Hyper-V TSC page statically").

The bot has tested the following trees: v5.5.11, v5.4.27.

v5.5.11: Failed to apply! Possible dependencies:
    0af3e137c144 ("clocksource/drivers/hyper-v: Untangle stimers and timesync from clocksources")
    ddc61bbc4501 ("clocksource/drivers/hyper-v: Reserve PAGE_SIZE space for tsc page")

v5.4.27: Failed to apply! Possible dependencies:
    0af3e137c144 ("clocksource/drivers/hyper-v: Untangle stimers and timesync from clocksources")
    ddc61bbc4501 ("clocksource/drivers/hyper-v: Reserve PAGE_SIZE space for tsc page")


NOTE: The patch will not be queued to stable trees until it is upstream.

How should we proceed with this patch?

-- 
Thanks
Sasha

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@gmail.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@vger.kernel.org
>> Signed-off-by: Yubo Xie <yuboxie@microsoft.com>
>> Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.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@microsoft.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 = {
> 

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

[Vitaly Kuznetsov]

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

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

[Dexuan Cui]

> From: linux-hyperv-owner@vger.kernel.org
> <linux-hyperv-owner@vger.kernel.org> On Behalf Of Yubo Xie
> Sent: Tuesday, March 24, 2020 8:20 AM
> ...
> sched clock callback should return time with nano second as unit
> but current hv callback returns time with 100ns. Fix it.

Hi Yubo,
I'm curious how you found the bug? :-) Did you notice some kind of symtom?

Thanks,
-- Dexuan

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

[Yubo Xie]

I use "time" to run some performance tests in our project under WSL2, but the result looks weird:  the value of "real" is far from the sum of "user" + "sys".

-----Original Message-----
From: Dexuan Cui <decui@microsoft.com> 
Sent: Wednesday, March 25, 2020 11:46 AM
To: Yubo Xie <ltykernel@gmail.com>; KY Srinivasan <kys@microsoft.com>; Haiyang Zhang <haiyangz@microsoft.com>; Stephen Hemminger <sthemmin@microsoft.com>; Wei Liu <liuwe@microsoft.com>; daniel.lezcano@linaro.org; tglx@linutronix.de; Michael Kelley <mikelley@microsoft.com>
Cc: Yubo Xie <yuboxie@microsoft.com>; linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org; vkuznets <vkuznets@redhat.com>; stable@vger.kernel.org; Tianyu Lan <Tianyu.Lan@microsoft.com>
Subject: RE: [PATCH] x86/Hyper-V: Fix hv sched clock function return wrong time unit

> From: linux-hyperv-owner@vger.kernel.org
> <linux-hyperv-owner@vger.kernel.org> On Behalf Of Yubo Xie
> Sent: Tuesday, March 24, 2020 8:20 AM
> ...
> sched clock callback should return time with nano second as unit but 
> current hv callback returns time with 100ns. Fix it.

Hi Yubo,
I'm curious how you found the bug? :-) Did you notice some kind of symtom?

Thanks,
-- Dexuan