Re: [PATCH 1/1] cpufreq: pcc-cpufreq: Re-introduce deadband effect to reduce number of frequency changes

[Andreas Herrmann <aherrmann@suse.com>]

On Wed, Oct 05, 2016 at 10:47:53AM +0530, Viresh Kumar wrote:
> Sorry for being late Andreas :(
> 
> On 14-09-16, 16:56, Andreas Herrmann wrote:
> 
> First of all, thanks for your hardwork in getting these numbers out.
> Really appreciate it.
> 
> > Below is some trace data. I hope it is of some help.
> > 
> > (A) - sampling 10s period when system is idle
> > (B) - sampling 10s period when system partially loaded (kernel
> >       compilation using 2 jobs)
> > 
> > (1) 4.8-rc5
> > (2) 4.8-rc5 with my patch (reintro of deadband effect within
> >     pcc-cpufreq)
> > (3) 4.8-rc5 with reversal of 6393d6a102 (cpufreq: ondemand: Eliminate
> >     the deadband effect)
> > 
> > Let me know whether you are looking for other trace data wrt this
> > issue.
> > 
> > 
> > Thanks,
> > 
> > Andreas
> > 
> > ---
> > 
> > (A)-(1)
> > 
> >  # Total Lost Samples: 0
> >  # Samples: 41  of event 'power:cpu_frequency'
> >  # Event count (approx.): 41
> >  # Overhead  Command       Shared Object     Symbol                       
> >  # ........  ............  ................  .............................
> >      39.02%  kworker/14:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >      29.27%  kworker/0:0   [kernel.vmlinux]  [k] cpufreq_notify_transition
> >      19.51%  kworker/10:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       7.32%  kworker/5:2   [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       2.44%  kworker/23:2  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       2.44%  kworker/40:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> > 
> > (A)-(2)
> > 
> >  # Total Lost Samples: 0
> >  # Samples: 6  of event 'power:cpu_frequency'
> >  # Event count (approx.): 6
> >  # Overhead  Command       Shared Object     Symbol                       
> >  # ........  ............  ................  .............................
> >      33.33%  kworker/1:2   [kernel.vmlinux]  [k] cpufreq_notify_transition
> >      16.67%  kworker/16:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >      16.67%  kworker/22:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >      16.67%  kworker/26:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >      16.67%  kworker/33:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> > 
> > (A)-(3)
> > 
> >  # Total Lost Samples: 0
> >  # Samples: 7  of event 'power:cpu_frequency'
> >  # Event count (approx.): 7
> >  # Overhead  Command       Shared Object     Symbol                       
> >  # ........  ............  ................  .............................
> >      28.57%  kworker/58:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >      14.29%  kworker/19:2  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >      14.29%  kworker/20:2  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >      14.29%  kworker/22:2  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >      14.29%  kworker/23:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >      14.29%  kworker/35:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> > 
> > ---
> > 
> > (B)-(1)
> > 
> >  # Total Lost Samples: 0
> >  # Samples: 2K of event 'power:cpu_frequency'
> >  # Event count (approx.): 2382
> >  # Overhead  Command       Shared Object     Symbol                       
> >  # ........  ............  ................  .............................
> >       5.75%  kworker/0:0   [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       4.16%  kworker/12:2  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       3.11%  kworker/17:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       2.94%  kworker/2:1   [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       2.73%  kworker/19:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       ...
> > 
> > (B)-(2)
> > 
> >  # Total Lost Samples: 0
> >  # Samples: 320  of event 'power:cpu_frequency'
> >  # Event count (approx.): 320
> >  # Overhead  Command       Shared Object     Symbol                       
> >  # ........  ............  ................  .............................
> >       4.69%  kworker/56:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       4.06%  kworker/12:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       4.06%  kworker/28:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       4.06%  kworker/6:2   [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       3.75%  kworker/32:2  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       ...
> > 
> > (B)-(3)
> > 
> >  # Total Lost Samples: 0
> >  # Samples: 333  of event 'power:cpu_frequency'
> >  # Event count (approx.): 333
> >  # Overhead  Command       Shared Object     Symbol                       
> >  # ........  ............  ................  .............................
> >       4.80%  kworker/51:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       4.50%  kworker/39:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       4.20%  kworker/47:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       3.90%  kworker/59:1  [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       3.90%  kworker/7:2   [kernel.vmlinux]  [k] cpufreq_notify_transition
> >       ...
> 
> I am worried by all of these.. So, its not the DVFS transition which
> took time, but cpufreq_notify_transition(). And probably one of the
> drivers in your setup is screwing up here, which has registered with
> cpufreq_register_notifier().
> 
> Can you please take a look at that ? Just check which all routines are
> getting called as part of srcu_notifier_call_chain().

I'll take a look into this.

> Also a simple (hacky) solution to fix the problem you have got is to
> divide the range of frequency in steps (which you have already done
> AFAICT in one of your patches) and not mention the frequencies that
> were part of the deadband earlier. That will keep the CPU at either
> low freq or some higher freqs.

Yes, seems worth to try this.

> But I am quite sure that we have an abuser here and we better find it
> now.


Thanks,

Andreas