[pulseaudio-tickets] [Bug 84585] Issue of CPU usage with HiFiBerry driver snd_soc_hifiberry_amp with Debian Wheezy kernel 3.12.28

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=84585

--- Comment #11 from Alessandro Ferri <alessandroferri_015 at fastwebnet.it> ---
About the frequency of the CPU, I have checked the parameters of current, max
and min cpu freq, these are the results:

pi at raspberrypi ~ $ sudo cat
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
700000
pi at raspberrypi ~ $ sudo cat
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq
700000
pi at raspberrypi ~ $ sudo cat
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq
700000

I have also tried to change the configuration parameters of the CPU
/boot/config.txt, in this manner: 

# Meaningful word.. This means 'enable cpu freq scaling'
force_turbo=0
# Set lowest cpu freq. By default, it's 700.
arm_freq_min=700

or

#uncomment to overclock the arm. 700 MHz is the default.
arm_freq=800

# for more options see http://elinux.org/RPi_config.txt

# Meaningful word.. This means 'enable cpu freq scaling'
force_turbo=0
# Set lowest cpu freq. By default, it's 700.
arm_freq_min=800

with these results:

pi at raspberrypi ~ $ sudo cat
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
700000
pi at raspberrypi ~ $ sudo cat
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq
800000
pi at raspberrypi ~ $ sudo cat
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq
700000


but the problem of the excessive use of cpu by pulseaudio remains and persists.
I do not think it is due to a low cpu speed setting.





(In reply to Tanu Kaskinen from comment #8)
> One important difference is that the configured sink latency is much lower
> with 3.12.25 than with 3.12.28. I don't know how the kernel could affect
> that, though, except by varying the maximum sink buffer size, but in this
> case it seems that with both kernels the sink buffer size is the same.
> 
> The configured sink latency is determined by what applications request. In
> this case there are shairport and LightSone connected to the sink (LightSone
> is actually connected to the monitor source of the sink, but if LightSone
> requests low latency from the source, that request will propagate to the
> monitored sink also). If shairport or LightSone have different latency
> configuration between the kernels, that would explain the difference in the
> configured sink latency. (The configured latency of the monitor source is
> the same in both cases, though, which suggests that LightSone is not to
> blame here). To get information about what latencies the applications
> request, you could attach (as an attachment, not in the comment!) the
> verbose log of pulseaudio in both cases. See
> https://wiki.ubuntu.com/PulseAudio/Log for instructions.
> 
> It's unexpected that lower latency leads to lower cpu use. Is it possible
> that the cpu runs at a lower speed with 3.12.28, causing higher figures in
> top? Here is some information about cpu speed scaling on Raspberry Pi:
> http://with-raspberrypi.blogspot.com/2014/03/cpu-frequency.html

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