[mythtv-users] glitchy audio with vdpau

[Alex Williamson]

On Wed, Mar 25, 2009 at 6:17 AM, Johnny <jarpublic at gmail.com> wrote:
>>> Thanks for the reference.  I typically only use the extra buffering,
>>> but thought I'd go through all the options given the problems I'm
>>> seeing.  FWIW, I've also discovered setting my minimum cpufreq scaling
>>> to 1.8GHz is enough to avoid the glitches.  Is there already some
>>> facility in mythtv to run an external script at the start and end of
>>> video playback?  Thanks,
>>>
>>> Alex
>>
>> you should set your cpu_governor to "conservative" and that should be
>> enough. "conservative" changes cpu speed very fast and very reliable.
>>
>> echo conservative > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

I tried this, the conservative governor will also make the CPU run at
1GHz, which causes the glitches.  Cpufreq scaling is based on
processor load, which is low, and has no notion of how much memory
bandwidth is being used by other hardware.

> Just curious how would this change the memory bandwidth? I thought the
> cpu scaling was only changing the multiplier that the cpu uses
> internally. It doesn't change the front side bus speed (ie the speed
> the memory is running at). Does it also mess with the memory in some
> way? Or is this a result of the fact that AMD has their memory
> controller on die with the CPU?

I haven't found a good reference that describes the problem, but the
memory controller is on the processor.  The memory controller seems to
be run based on a multiplier of the CPU frequency, but I don't know
what happens to that multiplier when processor frequency scaling
changes.  My system is running dual-channel ddr2/800, the problem is
apparently worse with slower memory or single channel memory.

Alex