[mythtv] [mythtv-commits] mythtv commit: r26286 by jyavenard

[Gavin Hurlbut]

On Tue, Sep 14, 2010 at 11:17 AM, Colin Guthrie <mythtv at colin.guthr.ie>wrote:

> Just for reference, I know that on Mandriva, Fedora and IIRC Ubuntu too,
> the default value for this is 4megs on HDA cards.
>
> $ cat /proc/asound/card0/pcm0p/sub0/prealloc
> 4096
>

This is probably done by pulseaudio setup.  I'm running on Ubuntu 10.04
Server with no pulseaudio, and it's 64.



> I didn't look at the code surrounding it, but I presume this is only
> tried when it's not big enough, e.g. if it's already set to 4096, then
> it wont be decreased down to 512?
>

My reading of the code is that the built-in prealloc writes are only to
increase the value, as there is no need to decrease.  And these writes
require write access to that file in proc, which basically means root
access.  I bumped mine to 512 manually as root (with nothing playing at the
time), and things have been mostly better.

Another thing that has reduced my underruns was rather unexpected.  The
scheduler query is pegging mysql to 100% CPU for like 10s or so.  To get
around that, I reniced mysql to 1.  I want mythfrontend to have priority
over the scheduling, but just so it will not glitch playback.  I'm on a
PentiumD, which is single HT core.  100% for mythcommflag (niced) and 100%
for mysql leaves nothing for the frontend.  With mysql niced, it's less
glitchy for me.  Alternatively, I could run mythfrontend niced -1, but I
like this better for now.


> Col
>
>
> --
>
> Colin Guthrie
> myth(at)colin.guthr.ie
> http://colin.guthr.ie/
>
> Day Job:
>  Tribalogic Limited [http://www.tribalogic.net/]
> Open Source:
>  Mandriva Linux Contributor [http://www.mandriva.com/]
>  PulseAudio Hacker [http://www.pulseaudio.org/]
>  Trac Hacker [http://trac.edgewall.org/]
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