[mythtv-users] [ATrpms-users] Confused: why did video performance DECREASE (up to 70%) after upgrading video card by 2 generations??? Please validate my analysis

Jeffrey J. Kosowsky mythtv-users at kosowsky.org
Mon Dec 8 04:39:08 UTC 2008


George Mari wrote at about 21:55:00 -0600 on Sunday, December 7, 2008:
 > Jeffrey J. Kosowsky wrote:
 > 
 > [deleted]
 > > 
 > > Instead I got the following:
 > > 
 > >                   GF4600            GeForce 6200
 > >                   ______            ____________________________
 > > glxgears          4700 fps          1360 fps (decrease by 70%!!!)
 > > quake3 demo       203 fps           74 fps (decrease by 64%)
 > > 
 > > 
 > > In mythtv, the visual performance is about the same even though the
 > > older 4600 had mythfrontend using 80% of CPU on HD programs vs about
 > > 40% for the newer 6200. 
 > 
 > Uhmmm...isn't this a good thing?  Doesn't this mean your 6200 is better 
 > for video than your old card?

I would have thought so -- but the actual playback quality is no
better -- I get the same slow video and audio pauses with "WriteAudio:
buffer underruns" every 1-2 seconds.

It's almost as if there is something standing in the way and keeping
the actual video output slow (and lagging relative to audio) despite
the fact that there is apparently enough CPU and video bandwidth
(based on the experiences of others with the 6200 card).

I only quoted the glxgears and quake3 benchmarks because I was surprised
at how much faster my 6 year old card is at those and wondered whether
that could be related to the problem -- i.e. maybe something is
holding the 6200 back from its full performance. Should the 6200
scores really be that much lower or could the card be stuck in some
type of low power mode? (note it is not overheating since at least per
nvidia-settings, the temp is stable at 46 degrees C, which is
consistent with my touch)

 > > In both cases it seems like the video lags the
 > > sound with the sound pausing every few seconds to wait for the "slower
 > > motion" video to catch up giving the sound a jerky appearance.
 > > 
 > > Also with the older card when viewing HD programs (but not SD
 > > programs) I got a lot of "NVP: prebuffering pause" errors in addition
 > > to the "WriteAudio: buffer underruns" that occur with each sound
 > > pause. I assume this is consistent with the fact that CPU usage is
 > > becoming a bottleneck on the 4600 for HD.
 > > 
 > > I tried the GeForce 6200 with the 96.xx, 173.xx, and 177.xx drivers
 > > without any difference.
 > > The GF4600 only works with the 96.xx drivers.
 > > 
 > > Both cards have glx working with direct rendering
 > > Both are AGP 4x with SBA and Fast Write turned on (same behavior with
 > > it off too).
 > > Both have XvMC on (though XvMC seems to only affect cpu usage and does
 > > not improve or worsen the video itself with the 6200)
 > 
 > Try turning off Xvmc with the 6200.  You might not need it.  Don't go by 
 > strictly by CPU usage - go by, "does the video look nice and smooth with 
 > no stuttering?"  XvMC isn't meant to change the quality of the video - 
 > just make it possible for marginal CPUs to decode video that otherwise 
 > cannot.  The problem is it's not perfect - it's a little harder to live 
 > with than plain Xv decoding, as far as things like OSD appearance, 
 > setup, fewer de-interlacing options, etc.

I tried with and without XvMC. The reason I have been using XvMC is to
"prove" (mostly to myself) that my old P4 2.8GHZ cpu is not an issue
since the total CPU usage maxes out at about 60-65% with XvMC% (and
maybe 70-80% without). In both cases, the picture looks good except
for the fact that it is a tad "slow" causing it to get behind the
audio and then for the audio to pause noticeably every second or so
while it waits for video to catch up.

 > 
 > > Both are using identical xorg.conf (with UseEvents=True and
 > > XvmcUsesTextures=False).
 > > Both have NvAGP=1 (though changing to the kernel agppart didn't make
 > > any difference).
 > > 
 > > So, it seems to me that either the 6200 is a bum card or I must be
 > > missing some configuration to unleash its power. 
 > > 
 > 
 > [deleted]
 > Your 6200 isn't a bum card - it's just that it's recommended a lot on 
 > this list as the least expensive card that is still effective at 
 > accelerated video decoding for SD and HD, and has good quality video 
 > output, and different options for rendering, such as OpenGl.  Nobody 
 > said it was a knock-your-socks off card for gaming.
 > 

I didn't mean "bum" in a pejorative sense -- just that I bought the
card based on the recommendation of several posters that it would be
better than my existing GF4 4600 card and would allow me to watch
SD/HD without serious artifacts. Now, after tens of hours of fiddling
and googling, I have not succeeded in getting this card to work any
better than my original old one -- in that there seems to be some
bottleneck remaining.

Nothing I do seems to improve the base problem of slow video and
pausing audio -- so I am frustrated that I can't get this to work.

 > The clock speed, memory bandwidth, marketing numbers, etc. of the card 
 > have no bearing on the performance of the video overlay used for video 
 > decode and acceleration - either for Xv or Xvmc.  That's my 
 > understanding, anyway.  As far as I know, there is no absolute spec of 
 > video decoding performance for any video card, at least as it relates to 
 >   our usage for MythtV.  The closest thing would be the table listed on 
 > Mythtv wiki under the subject: Xvmc.
 > 
 > My advice - if your looking for better gaming performance, get a better 
 > gaming card.  Something in the 7xxx series from Nvidia is still 
 > available for AGP.  It will still be "good enough" for displaying video.

I honestly have no interest in games and don't even have any on my system
except for an old version of Quake3 that I use only for testing. I
just want to watch HD on my computer monitor without having to upgrade
my whole machine -- unfortunately, it's either impossible with my
hardware setup or I'm just too dumb to figure it out.

But based on the experiences of others, I can't see why I can't get it
to work at least with a stripped down version of features.

Again I have a:
	Asus P4PE motherboard with 2GB DDR333MHz RAM
	P4 2.8GHz CPU
	eVGA 6200 256MB AGP card (running at 4x)
	pchdtv 5500 capture card (plus an older WinFast 2000XP Deluxe
		 Analog card that I don't really use)

	I'm willing to make sacrifices to resolution and refresh to get a
	stable and synchronized picture + audio, I just need some
	direction because I'm out of new ideas to try...


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