[mythtv-users] CONFIG_HZ setting in Linux kernel improved video playback for me

Jarod Wilson lists at wilsonet.com
Tue Feb 13 14:20:16 UTC 2007

Scott wrote:
> Greets.
> Like many MythTV Gentoo users I've built my own kernel. I have a  
> fairly hefty FE/BE box (core2 6600, 1GB RAM, SATA 500GB drive, Nvidia  
> 7600GT) that is primarily used for HDTV recording and DVD watching.  
> The problem was I was still not seeing butter-smooth video,  
> especially when the camera would pan across the screen. The problem  
> was noticeable on both DVDs and HDTV sources.
> Reading up on the 2.6.20 kernel changes I found this i386 kernel change:
> 	300Hz support. It is useful to have 300Hz support
> 	when doing multimedia work: 250 is fine for us in
> 	Europe but the US frame rate is 30fps (29.99 blah for
> 	pedants). 300 gives us a tick divisible by both 25 and 30,
> 	and for interlace work 50 and 60. It's also giving similar
> 	performance to 250Hz.
> I rebuilt my 2.6.20 kernel changing CONFIG_HZ from the default 100Hz  
> to 300Hz and happily saw butter-smooth video playback for both HDTV  
> and DVDs.
> Chances are this is my own fault as I'm sure the Gentoo stock kernels  
> are already set to 1000Hz or 512Hz like FC kernels used to be. So as  
> a tip, if you're trying various tweaks to improve your video playback  
> and building kernels on Gentoo, don't forget to check your CONFIG_HZ  
> setting as I forgot to.

250 and 1000 were previously your only choices unless you had some extra 
patching. I'm currently using 1000Hz Fedora kernels without a problem, 
but the real wave of the future it tickless kernels. Coming Real Soon 
Now. :)

Jarod Wilson
jarod at wilsonet.com

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