[mythtv-users] How to minimize CPU usage

[Jerry Rubinow]

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