Frequency not returning to fixed value after AVX workload

Frequency not returning to fixed value after AVX workload

[Hernandez Lopez, Fabiola]

Hi, 

We are seeing an unexpected behavior after applying AVX workloads. 
After setting the CPU frequency to a fixed value with CPU Freq - userspace governor and applying heavy AVX workloads, the CPU frequency is decreased (as expected) but it never returns to the previously established value. This does not happen on all cores, only on a single core. The only way to return to the desired frequency is by setting it through the command line again. 

We are wondering how can this change in frequency happen.

Thanks,

Fabiola

Re: Frequency not returning to fixed value after AVX workload

[Rafael J. Wysocki]

On Friday, October 11, 2019 7:45:55 PM CEST Hernandez Lopez, Fabiola wrote:
> Hi, 
> 
> We are seeing an unexpected behavior after applying AVX workloads. 
> After setting the CPU frequency to a fixed value with CPU Freq - userspace
> governor and applying heavy AVX workloads, the CPU frequency is decreased
> (as expected) but it never returns to the previously established value.

How do you measure the frequency?

> This does not happen on all cores, only on a single core. The only way to
> return to the desired frequency is by setting it through the command line
> again.

What exactly do you do to get the expected frequency back?

> We are wondering how can this change in frequency happen.

Is the target frequency in the turbo range?

RE: Frequency not returning to fixed value after AVX workload

[Hernandez Lopez, Fabiola]

How do you measure the frequency?
With lscpu.

What exactly do you do to get the expected frequency back?
A script is used that sets the frequency with /sys/devices/system/cpu/cpu*/cpufreq/scaling_setspeed

Is the target frequency in the turbo range?
No, the target frequency is the same as the base processor frequency: 2.4GHz. The max turbo frequency for this CPU si 3.9 GHz.
This has been tested with turbo boost enabled and disabled. 

This behavior is very sporadic: < 10%

Thanks,
Fabiola

-----Original Message-----
From: Rafael J. Wysocki [mailto:rjw@rjwysocki.net] 
Sent: Monday, October 14, 2019 4:45 AM
To: Hernandez Lopez, Fabiola <fabiola.hernandez.lopez@intel.com>
Cc: linux-pm@vger.kernel.org; Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Subject: Re: Frequency not returning to fixed value after AVX workload

On Friday, October 11, 2019 7:45:55 PM CEST Hernandez Lopez, Fabiola wrote:
> Hi,
> 
> We are seeing an unexpected behavior after applying AVX workloads. 
> After setting the CPU frequency to a fixed value with CPU Freq - 
> userspace governor and applying heavy AVX workloads, the CPU frequency 
> is decreased (as expected) but it never returns to the previously established value.

How do you measure the frequency?

> This does not happen on all cores, only on a single core. The only way 
> to return to the desired frequency is by setting it through the 
> command line again.

What exactly do you do to get the expected frequency back?

> We are wondering how can this change in frequency happen.

Is the target frequency in the turbo range?

Re: Frequency not returning to fixed value after AVX workload

[Srinivas Pandruvada]

On Mon, 2019-10-14 at 21:11 +0000, Hernandez Lopez, Fabiola wrote:
> How do you measure the frequency?
Do whatever you are doing to get to your problem state and while doing
the test run in another window:

#turbostat

Attach the output.

Thanks,
Srinivas

> With lscpu.
> 
> What exactly do you do to get the expected frequency back?
> A script is used that sets the frequency with
> /sys/devices/system/cpu/cpu*/cpufreq/scaling_setspeed
> 
> Is the target frequency in the turbo range?
> No, the target frequency is the same as the base processor frequency:
> 2.4GHz. The max turbo frequency for this CPU si 3.9 GHz.
> This has been tested with turbo boost enabled and disabled. 
> 
> This behavior is very sporadic: < 10%
> 
> Thanks,
> Fabiola
> 
> -----Original Message-----
> From: Rafael J. Wysocki [mailto:rjw@rjwysocki.net] 
> Sent: Monday, October 14, 2019 4:45 AM
> To: Hernandez Lopez, Fabiola <fabiola.hernandez.lopez@intel.com>
> Cc: linux-pm@vger.kernel.org; Srinivas Pandruvada <
> srinivas.pandruvada@linux.intel.com>
> Subject: Re: Frequency not returning to fixed value after AVX
> workload
> 
> On Friday, October 11, 2019 7:45:55 PM CEST Hernandez Lopez, Fabiola
> wrote:
> > Hi,
> > 
> > We are seeing an unexpected behavior after applying AVX workloads. 
> > After setting the CPU frequency to a fixed value with CPU Freq - 
> > userspace governor and applying heavy AVX workloads, the CPU
> > frequency 
> > is decreased (as expected) but it never returns to the previously
> > established value.
> 
> How do you measure the frequency?
> 
> > This does not happen on all cores, only on a single core. The only
> > way 
> > to return to the desired frequency is by setting it through the 
> > command line again.
> 
> What exactly do you do to get the expected frequency back?
> 
> > We are wondering how can this change in frequency happen.
> 
> Is the target frequency in the turbo range?
> 
> 
> 

RE: Frequency not returning to fixed value after AVX workload

[Hernandez Lopez, Fabiola]

Thanks, our engineer is trying to collect the info.
I'll write back with the data. 

Fabiola
-----Original Message-----
From: Srinivas Pandruvada [mailto:srinivas.pandruvada@linux.intel.com] 
Sent: Monday, October 14, 2019 4:23 PM
To: Hernandez Lopez, Fabiola <fabiola.hernandez.lopez@intel.com>; Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: linux-pm@vger.kernel.org
Subject: Re: Frequency not returning to fixed value after AVX workload

On Mon, 2019-10-14 at 21:11 +0000, Hernandez Lopez, Fabiola wrote:
> How do you measure the frequency?
Do whatever you are doing to get to your problem state and while doing the test run in another window:

#turbostat

Attach the output.

Thanks,
Srinivas

> With lscpu.
> 
> What exactly do you do to get the expected frequency back?
> A script is used that sets the frequency with 
> /sys/devices/system/cpu/cpu*/cpufreq/scaling_setspeed
> 
> Is the target frequency in the turbo range?
> No, the target frequency is the same as the base processor frequency:
> 2.4GHz. The max turbo frequency for this CPU si 3.9 GHz.
> This has been tested with turbo boost enabled and disabled. 
> 
> This behavior is very sporadic: < 10%
> 
> Thanks,
> Fabiola
> 
> -----Original Message-----
> From: Rafael J. Wysocki [mailto:rjw@rjwysocki.net]
> Sent: Monday, October 14, 2019 4:45 AM
> To: Hernandez Lopez, Fabiola <fabiola.hernandez.lopez@intel.com>
> Cc: linux-pm@vger.kernel.org; Srinivas Pandruvada < 
> srinivas.pandruvada@linux.intel.com>
> Subject: Re: Frequency not returning to fixed value after AVX workload
> 
> On Friday, October 11, 2019 7:45:55 PM CEST Hernandez Lopez, Fabiola
> wrote:
> > Hi,
> > 
> > We are seeing an unexpected behavior after applying AVX workloads. 
> > After setting the CPU frequency to a fixed value with CPU Freq - 
> > userspace governor and applying heavy AVX workloads, the CPU 
> > frequency is decreased (as expected) but it never returns to the 
> > previously established value.
> 
> How do you measure the frequency?
> 
> > This does not happen on all cores, only on a single core. The only 
> > way to return to the desired frequency is by setting it through the 
> > command line again.
> 
> What exactly do you do to get the expected frequency back?
> 
> > We are wondering how can this change in frequency happen.
> 
> Is the target frequency in the turbo range?
> 
> 
>