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Old 01-17-08, 02:02 PM   #1
uberjay
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Join Date: Jan 2008
Posts: 2
Question High CPU usage in X server at 24Hz refresh

Hey everyone.

I'm having a strange problem with a low refresh rate for my HTPC. I'm trying to get 1080p24 working. (1920x1080 @ 24Hz). This is a supported mode for my display, and my nvidia hardware (GForce 7050 PV) seems to support it as well. The EDID information dumped on X startup looks like this:

Code:
(--) NVIDIA(0):   1920 x 1080 @ 24 Hz
(--) NVIDIA(0):     Pixel Clock      : 74.16 MHz
(--) NVIDIA(0):     HRes, HSyncStart : 1920, 2558
(--) NVIDIA(0):     HSyncEnd, HTotal : 2602, 2750
(--) NVIDIA(0):     VRes, VSyncStart : 1080, 1084
(--) NVIDIA(0):     VSyncEnd, VTotal : 1089, 1125
(--) NVIDIA(0):     H/V Polarity     : +/+
(--) NVIDIA(0):     CEA Format       : 32
My display is a Sony KDL-46XBR4. I had to tell the nvidia driver to ignore the VertRefresh range reported by the TV (which claims to support only 58.000-62.000 Hz) using:

Code:
Option         "ModeValidation" "DFP-0:NoVertRefreshCheck"
In the Screen section of /etc/X11/xorg.conf.

For more information about my setup and the symptoms, take a look at this avsforum post.

Now, I've finally tracked some some interesting data points:

* When running in 24Hz refresh mode, the CPU usage of the X server is very high--every time I experience strange frame skipping issues (see that avsforum post for more information on what the skips look like...), the X server is consuming an entire CPU core.

* The CPU usage is not consistently high. In other words, playing back the same sequence of video sometimes will play without glitches, and other times will not.

* When the video is playing without glitches, it looks VERY smooth (because the refresh rate is matched with the fps of the video), yet the CPU usage of the X server is still hovering around 40-50%.

* When using a 60Hz refresh mode, the X server never consumes more than 5% (and usually is using less). In this case, there are no frame glitches, but because of the fps/refresh mismatch there is some visible judder. (sad)

For reference, I am using mplayer with the XV video output driver, and have sync to vblank enabled (with nvidia-settings). I'm using the latest ndriver release (169.07). Attached are the zipped results of nvidia-bug-report.sh.

Any helpful information would be greatly appreciated.

EDIT: This comment mentions this exact issue, but apparently it is also an issue for 50Hz (I haven't got that far yet... heh). I wonder if there is a way to determine if the nvidia driver is at fault, or the X server is at fault? Profiling perhaps? Maybe someone on the inside at NVidia has some ideas.
Attached Files
File Type: zip nvidia-bug-report.log.zip (29.5 KB, 157 views)
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