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Old 08-17-06, 04:23 AM   #13
quokka1
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Default Re: Poor Xinerama Performance

I stupidly omitted the bug report log from the archive. Here is the correct one.
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Old 08-17-06, 01:48 PM   #14
netllama
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Default Re: Poor Xinerama Performance

The attached bug report indicates that you're using 1.0-8178, not 1.0-8762 (which doesn't require any patches). I'd like to see a bug report against 1.0-8762.

Also, note the following warnings in your X log, which would certainly explain high CPU usage:
(WW) NVIDIA(2): The GPU driving screen 2 is incompatible with the rest of the
(WW) NVIDIA(2): GPUs composing the desktop. OpenGL rendering will be
(WW) NVIDIA(2): disabled on screen 2.
(WW) NVIDIA(3): The GPU driving screen 3 is incompatible with the rest of the
(WW) NVIDIA(3): GPUs composing the desktop. OpenGL rendering will be
(WW) NVIDIA(3): disabled on screen 3.
(WW) NVIDIA(4): The GPU driving screen 4 is incompatible with the rest of the
(WW) NVIDIA(4): GPUs composing the desktop. OpenGL rendering will be
(WW) NVIDIA(4): disabled on screen 4.
(WW) NVIDIA(5): The GPU driving screen 5 is incompatible with the rest of the
(WW) NVIDIA(5): GPUs composing the desktop. OpenGL rendering will be
(WW) NVIDIA(5): disabled on screen 5.

I was under the impression that the test app that you were providing was going to provide a quantifiable measurement of performance, and it seems that your determination is based on comparing CPU usage, which will likely be specific to your hardware setup. Do you have a measurable way of benchmarking this performance?

Also, is the performance problem evident if you're using just two displays with Xinerama?

Thanks,
Lonni
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Old 08-17-06, 08:40 PM   #15
quokka1
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Default Re: Poor Xinerama Performance

Quote:
Originally Posted by netllama
The attached bug report indicates that you're using 1.0-8178, not 1.0-8762 (which doesn't require any patches). I'd like to see a bug report against 1.0-8762.

Also, note the following warnings in your X log, which would certainly explain high CPU usage:
(WW) NVIDIA(2): The GPU driving screen 2 is incompatible with the rest of the
(WW) NVIDIA(2): GPUs composing the desktop. OpenGL rendering will be
(WW) NVIDIA(2): disabled on screen 2.
(WW) NVIDIA(3): The GPU driving screen 3 is incompatible with the rest of the
(WW) NVIDIA(3): GPUs composing the desktop. OpenGL rendering will be
(WW) NVIDIA(3): disabled on screen 3.
(WW) NVIDIA(4): The GPU driving screen 4 is incompatible with the rest of the
(WW) NVIDIA(4): GPUs composing the desktop. OpenGL rendering will be
(WW) NVIDIA(4): disabled on screen 4.
(WW) NVIDIA(5): The GPU driving screen 5 is incompatible with the rest of the
(WW) NVIDIA(5): GPUs composing the desktop. OpenGL rendering will be
(WW) NVIDIA(5): disabled on screen 5.

I was under the impression that the test app that you were providing was going to provide a quantifiable measurement of performance, and it seems that your determination is based on comparing CPU usage, which will likely be specific to your hardware setup. Do you have a measurable way of benchmarking this performance?

Also, is the performance problem evident if you're using just two displays with Xinerama?

Thanks,
Lonni
I will try just two screens with Xinerama. I did try 1.0-8762 with a 2.6.17 kernel and it was no better, but I will try again and post a bug report.

As for the OpenGL warnings, are these really relevent ? I'm not an expert here, but Java/Swing doen't use OpenGL unless you tell it to on the command line. I think it is experimental in JDK 1.5 and will become supported in Mustang (1.6).

I'm not 100% convinced that the AGP card is an NVS 280 (maybe 200 ?). Is there an easy way to identify it ? If it was a 200 would this cause the OpenGL warnings ?

Here is the lspci output for the AGP card:

0000:01:00.0 VGA compatible controller: nVidia Corporation NV17GL [Quadro4 200/400 NVS] (rev a3)


The performance is so poor that you don't need to measure it - you can see it. The case where CPU utilization goes to 100% and the Java app cannot manage to update a JTextField 100 times a second is just plain wrong (by a couple of orders of magnitude) - on any modern processor. Whether this is a problem with the Nvidia driver, Xinerama, or some local config or hardware issue I can't say.

A final question. Could this be related to agpgart ? Is it worth giving the Nvidia version a try ?

Last edited by quokka1; 08-17-06 at 08:58 PM.
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Old 08-17-06, 10:54 PM   #16
quokka1
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Default Re: Poor Xinerama Performance

I have tried various Xinerama layouts:

One AGP Card, VGA, Two heads:

Java/Swing Unbuffered: OK
Java/Swing Double Buffered: OK
Firefox: OK



One AGP Card, VGA Two heads + One PCI Card, DVI, Two heads

Java/Swing Unbuffered: OK
Java/Swing Double Buffered: Poor (but not as bad as 6 heads)
Firefox: Not great (but not as bad as 6 heads)

Two PCI cards, all DVI, Four heads:

About the same as the AGP/PCI combo.



One PCI card, DVI two heads:

Java/Swing Unbuffered: OK
Java/Swing Double Buffered: Poor (but not as bad as 4 heads)
Firefox: Not Bad
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Old 08-17-06, 11:49 PM   #17
netllama
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Default Re: Poor Xinerama Performance

It sounds like you may be hitting bandwidth limits of the PCI bus.

-Lonni
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Old 08-18-06, 01:45 AM   #18
quokka1
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Default Re: Poor Xinerama Performance

Quote:
Originally Posted by netllama
It sounds like you may be hitting bandwidth limits of the PCI bus.

-Lonni
I don't believe so. If that were the case then why does the configuration of 3 x 2 TwinView exhibit good performance ? (3 Xinerama 'screens', each of which is a TwinView configuration of two heads).

And why does the 3x1 Xinerama configuration using 'nv' with three cards exhibit decent performance ?

And why do tests run on the AGP connected heads run much worse when there is a PCI card in the XInerama config ?
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Old 08-18-06, 11:54 AM   #19
netllama
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Default Re: Poor Xinerama Performance

When using TwinView (and performance is good), do you see this warning (or something similar) in your X log?
(WW) NVIDIA(2): The GPU driving screen 2 is incompatible with the rest of the
(WW) NVIDIA(2): GPUs composing the desktop. OpenGL rendering will be
(WW) NVIDIA(2): disabled on screen 2.

Adding a PCI card to the mix would likely reduce performance if you also had an AGP card because the PCI card is a bottleneck.

Thanks,
Lonni
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Old 08-18-06, 11:01 PM   #20
quokka1
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Default Re: Poor Xinerama Performance

The most 'interesting' piece of evidence is that on occasion top shows the 'si' field field of the CPU summary in the area of 80 - 90%. Presumably 'si' is softirq - it doesn't seem to be mentioneed in top's man page.

I very much doubt that it should ever reach this value on any running system. It seems most unlikely to me that this is due to PCI bus bandwidth limitations or not using OpenGL etc etc.

I read another thread about real time Linux, SMP issues. It is mentioned that some of the glue code is using semaphores in interrupt context. As the poster says, this is wrong and probably wrong on any OS. I'm not saying that this is neccessarily the cause of my performance issues, but given the high 'si' values it may be relevent. I will spend a little time looking at the code, understanging the patches etc.

Incidently I tried apci=off kernel boot option. It possibly made things slightly worse - certainly no better.
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Old 08-19-06, 12:29 AM   #21
quokka1
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Default Re: Poor Xinerama Performance

Quote:
Originally Posted by netllama
When using TwinView (and performance is good), do you see this warning (or something similar) in your X log?
(WW) NVIDIA(2): The GPU driving screen 2 is incompatible with the rest of the
(WW) NVIDIA(2): GPUs composing the desktop. OpenGL rendering will be
(WW) NVIDIA(2): disabled on screen 2.

Adding a PCI card to the mix would likely reduce performance if you also had an AGP card because the PCI card is a bottleneck.

Thanks,
Lonni
Yes, these messages are present with TwinView configured
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Old 08-21-06, 02:14 PM   #22
netllama
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Default Re: Poor Xinerama Performance

I've spent some time attempting to reproduce this problem. If I use two dis-similar GPUs, with Xinerama across 4 displays, such that I see the following warnings:
(WW) NVIDIA(2): The GPU driving screen 2 is incompatible with the rest of the
(WW) NVIDIA(2): GPUs composing the desktop. OpenGL rendering will be
(WW) NVIDIA(2): disabled on screen 2.

then I can reproduce the high CPU usage problem.

However, if I use two identical GPUs, with Xinerama across 4 displays, such that the above warnings are not present, then the problem is eliminated.

This points to the lack of OpenGL rendering support as the problem, as you're falling back to software, and thus, hitting the CPU for everything.

I'm afraid that there's no bug here. The solution to your problem is to use identical GPUs (or at least GPUs all from the same family) for all displays.

Thanks,
Lonni
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Old 09-03-06, 07:11 PM   #23
Alchemist
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Default Re: Poor Xinerama Performance

I have been experiencing this problem, too. In my case, it's an AGP FX 5200 and a PCI GF2 MX200.

I have a couple things to add:

1) TwinView (just the 5200) works perfectly.

2) Non-Xinerama (old-style multiple X screens) works perfectly.

3) OpenGL didn't appear to be the issue, as I wasn't running anything with OpenGL, removing glx from xorg.conf had no effect, and I wasn't getting the OpenGL error mentioned above.

Hope that helps someone. I've decided turning off Xinerama and using the old X style is good enough for me, so if you're having this problem, you might want to at least give it a try.
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