[mythtv-users] Fixed!: Nvidia Sync to Vblank pegging cpu in X

Steven Adeff adeffs.mythtv at gmail.com
Wed Dec 20 13:53:18 UTC 2006

On 12/19/06, Jim herold <jim.herold at comcast.net> wrote:
> On 12/17/06, J. Miller <mythtv.org at elvenhome.net> wrote:
> > > I've been fighting the scourge of myth causing X to consume 100% of the
> > > CPU when Xv Sync to Vblank is turned on in nvidia-settings.  Everything
> > > works just fine with it unchecked but that is the only sync setting that
> > > gives me a perfect picture with no tearing.  Myth's native OpenGL sync
> > > still tears a little.  The problem turned out to be the modeline I was
> > > using.  It was a 1368x768 56Hz modeline which apparently triggered the
> > > issue.  I switched to a 1360x768 60Hz modeline and now everything works
> > > peachy.  X still starts consuming large amounts of CPU occasionally but
> > > it quickly drops back down to the 2-4% range.  I'm not 100% sure that it
> > > was the refresh but a modeline change did the trick.  Hopefully posting
> > > this here will help point others that have the same problem in a new
> > > direction.
> > NVIDIA have added an option in (I think) 9626 to poll() instead of
> > for vblank, which fixes the high cpu usage when sync to vblank is switched
> > on. It's called "UseEvents".
> My Modeline was already 1280x720 @ 60Hz.  I've tried tweaking it a number of ways but
> never came up with a magic modeline that fixed the issue here.
> Never thought to try the sync to vblank setting (thanks also to Steven Adeff for this
> suggestion).  I knew it was recommended to disable that for XvMC, but never connected
> that it'd be a good idea for Xv as well.  With the sync to vblank off everything looks great
> on my setup, and the X cpu usage hovers around 10% when watching 720p content.
> I tried the "UseEvents" thing.  Interestingly, it works, but increases the "wa" cpu usage in
> top, and therefore leaves less cpu idle time by roughly 20% when compared with just
> disabling the sync to vblank.

normally the Xv Sync to vblank in nvidia-settings is what causes most
people's high Xorg cpu usage, so disabling it would fix that problem.
My, and from what I gather some others as well, issue was, doing this
would cause random tearing during very high motion camera pans, and a
constant warble-ish tear of the top 10% of the screen (not very
noticeable unless your looking for it, but still a problem). So I'm
hoping this will fix that, though I don't think I'll get the chance to
try it until next week (vacation).

One thing I did notice with using the 9xxx drivers was that X would
only let me use a 24hz 1080p modeline instead of the other builtin's I
use in 8776 (1920x1080_30 or 1920x1080_60). Which "works" with my tv,
it just causes other output issues since the video is 30hz... Perhaps
using an actual modeline will fix this. I'll have to play around and

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