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Old 08-14-06, 08:28 PM   #1
quokka1
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Default Poor Xinerama Performance

I have encountered some quite serious 2D performance problems with Xinerama and the Nvidia drivers.

Environment:

Athlon 2800 XP (Barton)
1 Gig Memory
1 x NVS 280 AGP card
2 x NVS 280 PCI cards

Kernal 2.6.15 + Nvidia driver 7167
--or--
Kernel 2.6.17.8 + Nvidia driver 8762 (with patches applied)

Xorg 6.8.1

Up to 6 x 19" LCDs all at 1280x1024, 24bit depth. Mixture of VGA and DVI.

Performance is more or less the same (poor) with either combination of kernel/driver. Performance also seems to degrade as more heads are added ie 2 heads perform better than 4 four heads and 4 heads are better than 6 heads. Performance seems to be independent of whether kernel premption is turned on/off.

I am mostly interested running Java (Swing) applications in this environment, but browser performance and other general performance are also important.

What I have been able to discover so far is that the issue is related to applications that do double buffering. Double buffering in Firefox can be turned off with the viewmanager.do_doublebuffering config option. Setting this to false results in greatly improved page rendering or page scrolling performance. However, there are too many rendering problems for this to be viable workaround.

Performance with Java (Swing) applications can be dramatically improved by turning off double buffering. I would estimate by a factor of 10 or more. For anybody interested, you can do this programmatically with

RepaintManager.currentManager (someComponent ).setDoubleBufferingEnabled (false)

It then stays off globally until turned back on.

Rendering of Swing dialogs etc is generally good (and fast) with double buffering turned off, but there is some flickering with for example text fields that are rapidly updated (several times a second).

So my questions are

1) Does anybody have further insight/explanation of the issues involved here or any references that might help ?

2) Is this related to the Nvidia drivers or purely a Xinerama issue ?
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Old 08-14-06, 08:49 PM   #2
quokka1
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Default Re: Poor Xinerama Performance

Some futher info that I omitted:

Motherboard is based on VIA KT880 chipset.

When double buffering is enabled, top shows very high values in the 'si' field of the CPU summary line. 'si' values can be in excess of 80% on some occasions.
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Old 08-14-06, 08:59 PM   #3
netllama
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Default Re: Poor Xinerama Performance

This is likely more due to Xinerama than the nvidia driver. Does the performance improve (with just two displays) if you switch to TwinView instead?

If you'd like to have this investigated further, please generate and attach an nvidia-bug-report.log, along with specific details on how to replicate the performance problems you're reporting. It would be especially helpful if you could provide some kind of benchmark so that we're comparing apples to apples.

Thanks,
Lonni
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Old 08-14-06, 09:31 PM   #4
quokka1
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Default Re: Poor Xinerama Performance

Quote:
Originally Posted by netllama
This is likely more due to Xinerama than the nvidia driver. Does the performance improve (with just two displays) if you switch to TwinView instead?

If you'd like to have this investigated further, please generate and attach an nvidia-bug-report.log, along with specific details on how to replicate the performance problems you're reporting. It would be especially helpful if you could provide some kind of benchmark so that we're comparing apples to apples.

Thanks,
Lonni

Lonni,

Thanks for the prompt reply. I will try just 2 heads with TwinView. If I undertand correctly, it's not a solution for more than two heads as it cant be used in conjuction with Xinerama.

As for a benchmark, I will write a small Java app that demonstrates the issues and post that along with your other requirements.
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Old 08-15-06, 12:57 AM   #5
quokka1
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Default Re: Poor Xinerama Performance

This post may or may not be related:

http://www.nvnews.net/vbulletin/showthread.php?t=74111
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Old 08-15-06, 06:06 AM   #6
quokka1
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Default Re: Poor Xinerama Performance

Upon some further investigation:

Two screens with TwinView are fine. Performance is good.

Six screens in a 2x3 grid using TwinView AND Xinerama are also fine and performance is little different from just two screens and TwinView. Just to clarify the setup here, Xinerama sees just three screens with TwinView combining each of three pairs of screens into one screen.

Six screens in a 2x3 grid using Xinerama only are very poor. Xinerama, in this case is presented with six individual screens. Performance is terrible with Java swing apps and poor with Firefox.

This seems to suggest that the problem may not be just with Xinerama, but quite possibly with the Nvidia driver.

TwinView plus Xinerama is not a viable option, as applications cannot find physical screen boundaries.

Last edited by quokka1; 08-15-06 at 07:08 AM.
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Old 08-15-06, 12:51 PM   #7
netllama
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Default Re: Poor Xinerama Performance

quokka1, I'm not clear how you concluded that the behavior you're seeing with Xinerama is an nvidia driver issue.

Does performance improve with the 'nv' X driver & Xinerama?
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Old 08-15-06, 07:11 PM   #8
quokka1
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Default Re: Poor Xinerama Performance

Quote:
Originally Posted by netllama
quokka1, I'm not clear how you concluded that the behavior you're seeing with Xinerama is an nvidia driver issue.

Does performance improve with the 'nv' X driver & Xinerama?
I can't get the nv driver to work for just 2 heads. It works with only the first head configured. When I configure the 2nd head on the first card, the X server dies with a "Resource Already in Use" message. Do you have a sample config for nv for just two heads on an AGP NVS 280 that is known to work ?

Here are the device sections that I am using for the AGP card:

Section "Device"
Identifier "Videocard1"
Driver "nv"
VendorName "Nvidia"
BoardName "Nvidia NVS280 AGP"
#Option "HWCursor" "off"
Option "CrtcNumber" "0"
Screen 0
BusID "PCI:1:0:0"
EndSection

Section "Device"
Identifier "Videocard2"
Driver "nv"
VendorName "Nvidia"
BoardName "Nvidia NVS280 AGP"
#Option "HWCursor" "off"
Option "CrtcNumber" "1"
Screen 1
BusID "PCI:1:0:0"
EndSection
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Old 08-15-06, 08:45 PM   #9
netllama
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Default Re: Poor Xinerama Performance

The nv X driver only supports one display per GPU. You should still be able to setup Xinerama across multiple GPUs to compare performance with the nvidia driver.

Thanks,
Lonni
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Old 08-15-06, 10:30 PM   #10
quokka1
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Default Re: Poor Xinerama Performance

Quote:
Originally Posted by netllama
The nv X driver only supports one display per GPU. You should still be able to setup Xinerama across multiple GPUs to compare performance with the nvidia driver.

Thanks,
Lonni
Seems like the nv driver doesn't support DVI either, but thats another story.

I set up three screens using VGA with xinerama and the 'nv' driver. Performance is better than the 'nvidia' driver with xinerama. In the case of a small java swing program I have written to demonstrate the problem, the nv driver with xinerama is vastly better than nvidia with xinerama. Performance with this program and nvidia + xinerama is terrible.

Perhaps it is time to submit a bug report with the test case unless there is anything else I can try ?
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Old 08-15-06, 11:19 PM   #11
netllama
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Default Re: Poor Xinerama Performance

Please attach your test case, along with details on how to measure the performance.

Thanks,
Lonni
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Old 08-16-06, 02:03 AM   #12
quokka1
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Default Re: Poor Xinerama Performance

Quote:
Originally Posted by netllama
Please attach your test case, along with details on how to measure the performance.

Thanks,
Lonni
Attached is zip file containing bug report, test case and notes.

Thanks
Attached Files
File Type: zip xinerama_performance.zip (9.4 KB, 96 views)
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