Re: [dpdk-dev] librte_power w/ intel_pstate cpufreq governor

[longtb5@viettel.com.vn]

Hi Dave,

Actually in my test lab which is a HP box running CentOS 7 on kernel version
3.10.0-693.5.2.el7.x86_64, the default cpufreq driver is pcc_cpufreq. So I guess 
disabling intel_pstate wouldn't help in my case.

# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
pcc-cpufreq

# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors 
conservative userspace powersave ondemand performance

According to kernel doc, pcc_cpufreq also doesn't export scaling_availabe_frequencies
in sysfs.

>From kernel doc:
"scaling_available_frequencies is not created in /sys. No intermediate
frequencies need to be listed because the BIOS will try to achieve any
frequency, within limits, requested by the governor. A frequency does not have
to be strictly associated with a P-state."

The lack of scaling_availabe_frequencies makes power_acpi_cpufreq_init() 
complains, similar to the problem with intel_pstate as  in the other thread.
I have tried (though with not much effort) to force the kernel
to use acpi-cpufreq instead but without success.

Luckily, as quoted above pcc_cpufreq supports setting of arbitrary frequency, 
so a simple workaround for now is to fake a scaling_available_frequencies file
in another directory, then edit the code in librte_power to use that file instead.

Regards,
-BL

> -----Original Message-----
> From: david.hunt@intel.com [mailto:david.hunt@intel.com]
> Sent: Monday, March 5, 2018 5:16 PM
> To: longtb5@viettel.com.vn; dev@dpdk.org
> Subject: Re: [dpdk-dev] librte_power w/ intel_pstate cpufreq governor
> 
> Hi BL,
> 
> I have always used "intel_pstate=disable" in my kernel parameters at boot so
> as to disable the intel_pstate driver, and force the kernel to use the acpi-
> cpufreq driver:
> 
> # cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
> acpi-cpufreq
> 
> This then gives me the following options for the governor:
> ['conservative', 'ondemand', 'userspace', 'powersave', 'performance',
> 'schedutil']
> 
> Because DPDK threads typically poll, they appear as 100% busy to the p_state
> driver, so if you want to be able to change core frequency down (as in l3fwd-
> power), you need to use the acpi-cpufreq driver.
> 
> I had a read through the docs just now, and this does not seem to be
> mentioned, so I'll do up a patch to give some information on the correct
> kernel parameters to use when using the power library.
> 
> Regards,
> Dave.
> 
> On 2/3/2018 7:20 AM, longtb5@viettel.com.vn wrote:
> > Forgot to link the original thread.
> >
> > http://dpdk.org/ml/archives/dev/2016-January/030930.html
> >
> > -BL
> >
> >> -----Original Message-----
> >> From: longtb5@viettel.com.vn [mailto:longtb5@viettel.com.vn]
> >> Sent: Friday, March 2, 2018 2:19 PM
> >> To: dev@dpdk.org
> >> Cc: david.hunt@intel.com; mhall@mhcomputing.net;
> >> helin.zhang@intel.com; longtb5@viettel.com.vn
> >> Subject: librte_power w/ intel_pstate cpufreq governor
> >>
> >> Hi everybody,
> >>
> >> I know this thread was from over 2 years ago but I ran into the same
> > problem
> >> with l3fwd-power today.
> >>
> >> Any updates on this?
> >>
> >> -BL
> >