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From: Andy Tang <andy.tang@nxp.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "rjw@rjwysocki.net" <rjw@rjwysocki.net>,
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>
Subject: RE: [EXT] Re: Ask for help about cpufreq issue
Date: Thu, 13 Feb 2020 08:18:15 +0000	[thread overview]
Message-ID: <VI1PR04MB43332FB8B9FAD91160D91A0CF31A0@VI1PR04MB4333.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <20200212115054.eouh7e42uqlcweo3@vireshk-i7>

Hi Viresh,

> -----Original Message-----
> From: Viresh Kumar <viresh.kumar@linaro.org>
> Sent: 2020年2月12日 19:51
> To: Andy Tang <andy.tang@nxp.com>
> Cc: rjw@rjwysocki.net; linux-pm@vger.kernel.org
> Subject: Re: [EXT] Re: Ask for help about cpufreq issue
> 
> Caution: EXT Email
> 
> On 12-02-20, 10:11, Andy Tang wrote:
> > Hi Viresh,
> >
> > I have another cpufreq issue on our lx2160a platform which has 16 cores
> and 8 clusters.
> >
> > Cpufreq works well for ondemand, performance governor.
> > But for conservative governor, even though cpu usage is almost zero,
> > but some cpus are not work on the lowest frequency sometimes. It keeps
> > bouncing from the lowest frequency to the other higher frequencies.
> > The defaut values are used for the tunable for conservative governor.
> > In summary, why cpu doesn't work at the lowest frequency even the cpu
> load is almost zero?
> >
> > root@lx2160ardb:/sys/devices/system/cpu# cat cpufreq/conservative/
> > down_threshold        freq_step             ignore_nice_load
> sampling_down_factor  sampling_rate         up_threshold
> > root@lx2160ardb:/sys/devices/system/cpu# cat cpufreq/conservative/*
> > 20
> 
> Try increasing down_threshold to a value of 50 (i.e. we reduce frequency if
> the load is below 50%) and see if it makes a difference.
I tried down_threshold = 50, it is better. But some cpus still don't work at the lowest frequency sometimes.

> 
> I believe something is running on the CPU, that you are unaware of.
> Try doing tracing to see what's going on all CPUs.
I keep monitoring cpu usage for several minutes, by top and mpstat tool, and found
most of the cpus are 100% idle, once in a while one of the cpus increases the load to about 18%.

Technically if the cpu usage is not more than up_threshold(80), cpu won't increase its frequency and keep
at the lowest frequency when cpu is at the lowest frequency and conservative governor is used. 
So I can't understand why cpu frequency increased?

Thanks,
Andy
> 
> --
> viresh

  reply	other threads:[~2020-02-13  8:19 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-07  5:09 Ask for help about cpufreq issue Andy Tang
2020-02-07  5:23 ` Viresh Kumar
2020-02-07  6:03   ` [EXT] " Andy Tang
2020-02-07  7:05     ` Viresh Kumar
2020-02-11  4:20       ` Andy Tang
2020-02-11  5:53         ` Viresh Kumar
2020-02-11  6:23           ` Andy Tang
2020-02-11  6:34             ` Viresh Kumar
2020-02-11  7:20               ` Andy Tang
2020-02-12 10:11               ` Andy Tang
2020-02-12 11:50                 ` Viresh Kumar
2020-02-13  8:18                   ` Andy Tang [this message]
2020-02-13  8:48                     ` Viresh Kumar
2020-02-13  9:12                       ` Andy Tang
2020-02-13  9:15                         ` Viresh Kumar
2020-02-13  9:21                           ` Andy Tang
2020-02-14 10:00                       ` Andy Tang
2020-02-17  8:22                         ` Viresh Kumar

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