[mythtv-users] How to minimize CPU usage

[Chris Ribe]

Reducing color depth certainly affects picture quality from a technical
standpoint, but it sounds like you are in a position where you may need
choose the lesser of several picture degrading evils.

720p is 30 frames/s. 1080i is 60 1920x540 fields/s.  Consider trying out
your FX5200 with reduced color depth, the bandwidth needs should be
significant;y reduced.

On 1/28/06, Jerry Rubinow <jerrymr at gmail.com> wrote:
>
> On 1/28/06, Kevin Kuphal <kuphal at dls.net> wrote:
> > Jerry Rubinow wrote:
> > > On 1/28/06, Kevin Kuphal <kuphal at dls.net> wrote:
> > >
> > >> Jerry Rubinow wrote:
> > >>
> > >>> I'm running myth with separate front/back end computers.  The
> frontend
> > >>> is a 2.8GHz P4 with 512MB ram, trying to display 720p HD, but I'm
> > >>> maxing out the CPU - myth ~65+%, X around 30+%.  The video is at
> times
> > >>> choppy when there's a lot of stuff changing in the frame.  What can
> I
> > >>> do to reduce CPU usage?
> > >>>
> > >>> Here's what I've done so far:
> > >>> -compiled myth with --enable-proc-opt (using SVN from less than a
> week ago)
> > >>> -using ratpoison for window manager
> > >>> -not using any deinterlacing
> > >>>
> > >>> Note: XvMC is not an option.
> > >>>
> > >>> I'm running FC4.
> > >>>
> > >>> mythfrontend -v playback reports that it's using Xvideo, format
> I420,
> > >>> using realtime priority, video timing method: RTC (glx vsync not
> > >>> supported in my driver).  Then I get a lot of video ahead of audio
> > >>> dropping frames messages, and then a lot of audio ahead of video
> > >>> messages.
> > >>>
> > >>> /proc/meminfo says there's 100MB free while running myth, so I guess
> > >>> it's not swapping.
> > >>>
> > >>> What might be causing the high CPU?  I've read about people with
> > >>> 2.4Ghz P4s not having a problem with HD, so it seems like there
> should
> > >>> be something I can do.  Would compiling my own kernel help?  With
> what
> > >>> options?  Anything else I can try first?
> > >>>
> > >>>
> > >> Try using libmpeg2 for your playback.  I'd suggest looking into
> > >> hyperthreading support in your kernel to see if it is enabled.  I
> > >> believe this means using an SMP kernel.  I'm not sure if that will
> make
> > >> a difference but it might.  And lastly, your video card and drivers
> do
> > >> help alot.  I've struggled with my choice of ATI on one of my
> frontends
> > >> and as I'm moving to HD, I'm biting the bullet and spending the $40
> on
> > >> an Nvidia FX card and it will be one of the best $40 I've spent on my
> > >> system as it means HD playback on my 2.4ghz Celeron with XvMC.
> > >>
> > >> Kevin
> > >>
> > >
> > > Sorry, I left out that I'm using libmpeg2.  Hyperthreading - hmm,
> > > unfortunately I just checked and my CPU doesn't support hyperthreading
> > > (it's a 533MHz bus 2.8GHz P4).  I tried going the FX 5200 route, only
> > > to discover that I I can't achieve the transfer speeds I need over PCI
> > > (my motherboard only has two slots, both PCI).  1280x720x(24 or 32)
> > > bits, 30 frames a second (or 60, even worse) - PCI's max throughput is
> > > 600 to 700 Mbits/sec.  I tried XvMC on the 5200 but it was always a
> > > bit glitchy.  The onboard graphics is AGP, but now instead of being
> > > limited by bus speed, it's by CPU speed.  Very frustrating, since it's
> > > soooo close to working properly.
> > >
> > >
> > Hmm.  I'm about to buy an FX5500 PCI for use in my frontend.  Are you
> > saying that you can't drive HD content to the PCI card because it is
> > PCI, not AGP?  I'm using XvMC on my MX440 AGP and it works great with
> > Myth and the 7676 Nvidia drivers on the SVN.  You might want to give
> > XvMC with that driver version another shot when 0.19 is released on your
> > FX5200.  I've found it to be very solid.
> >
> > Kevin
>
> When I was trying to do HD over the PCI FX5200, I consistently had
> slowness/skipped frames/stuttering.  I eventually did some
> calculations, and 720p at 24bits and 30 frames per second is 632
> Mbits/sec.  I saw in the list archives that PCI's maximum transfer
> speed ranges between 600-700 Mbits/sec.  However, I think 24 bit video
> is actually using 32 bips per pixels (alpha), and isn't HD refreshing
> at 60 frames/sec?  So I must not be figuring something right, or else
> I wouldn't be getting anything approaching viewable, but I was
> actually getting something pretty close, so I'm not entirely sure
> what's going on.  But in any case, it seems like at a minimum, it's
> close to PCI's capacity.
>
> As far as XvMC, I have no idea how the bandwidth of what's being
> pushed to the card for XvMC compares that of non-XvMC (although I
> would really like to know).  I do know I had various problems with
> XvMC displaying correctly.  Maybe due to bandwidth issues also, but I
> don't know.  But I will give it another shot at some point before I
> throw in the towel on this computer and relegate it to an SD frontend
> for the tv upstairs.
>
> -Jerry
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