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Old 04-03-06, 11:53 AM   #61
Linuxhippy
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Default Re: Slow AA text rendering in KDE

Quote:
Originally Posted by xorbe
So the next question is, how can we force software rendering of all fonts on Linux?
Well the fonts are currently software rendered and thats exactly why they are so slow (like the 30x slowdown on my fastest glyph-painting machine).
If you don't want software rendering for your fonts you have to disable it completly for all types of operations, which means using the VESA driver

So its normal that its way slower than normal font rendering, however I don't see a reason why a NV18 outperforms NV43 chip by about 3,5 times.

Quote:
Or get the nVidia driver fixed?
I don't know where the problem lies, my benchmark should just show that some guys definitifly _have_ problems with glyph painting performance.
My guess is that the NV4x chipset Nvidia does subpixel rendering using their onboard-shaders but something does not work as well as it should.

I am however curious why Nvidia stopped talking about this issue, the only comments I saw on this thread are one of those two types:
* We don't see a problem
* We can't reproduce a problem

This sounds a bit strange, especially keeping in mind that here were 3-4 guys who were able to reproduce it without any configuration change. (Doesn't nvidia run something like a performance regression testsuite before they release new drivers??)
So maybe its a hardware limitation they want to hide or they simply really don't care.

lg Clemens
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Old 04-03-06, 02:06 PM   #62
xorbe
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Default Re: Slow AA text rendering in KDE

Quote:
Originally Posted by Linuxhippy
Well the fonts are currently software rendered and thats exactly why they are so slow (like the 30x slowdown on my fastest glyph-painting machine).
If you don't want software rendering for your fonts you have to disable it completly for all types of operations, which means using the VESA driver
I don't follow. VESA was the fastest font-rendering mode across the board for me -- aren't they software-rendered in that mode?

Quote:
Originally Posted by Linuxhippy
So its normal that its way slower than normal font rendering, however I don't see a reason why a NV18 outperforms NV43 chip by about 3,5 times.
My WAG would be that NV43 offers a feature that NV18 doesn't, and it's getting blindly used, but it's actually slower than the software-only methed. I suppose we could crack open the QT code to see if the feature could be identified.

Last edited by xorbe; 04-03-06 at 03:02 PM.
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Old 04-03-06, 03:06 PM   #63
Linuxhippy
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Default Re: Slow AA text rendering in KDE

Quote:
Originally Posted by xorbe
I don't follow. VESA was the fastest font-rendering mode across the board for me -- aren't they software-rendered in that mode?
It could be that moden nvidia cards use shaders for subpixel-aa rendering so this description only applies to cards which do the subpixel-stuff in software like (i am quite sure) my NV18.

Subpixel-AA is always software-rendered if hardware does not provide features for accaleration (like my (fast) NV18 card). Wether you use VESA or the nvidia driver doesn't matter at all, rendering is done by the CPU.
The big difference is that with VESA everything is rendered into an surface (image) held in system-ram compared to the memory on your graphic card when using the accalerated nvidia driver.
If you now want to perform subpixel-aa you need to get the values of the desitantion surface (since the result is a composition of the glyph + destination surface + some logic for subpixel). This operation is quite fast for vesa because all the pixels are stored in RAM anyway where they can be accassed in a fast way by your CPU.
When using the nvidia driver the pixel-values have to be transferred from the board-memory to system-ram, then the composition takes place and afterwards the result needs to be uploaded to your video-card again.
The downside of the vesa driver is that it will perform quite poor comparing things your graphic-card can do in HW (like filling rects or blits).

Its the same problem all the time if you have graphic-hw solutions that have to do some things they can't do in hardware. You need the read-back the affected pixels into RAM and later send the result back to VRAM which is quite often much slower than the actual rendering done in software.


lg Clemens
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Old 04-03-06, 03:29 PM   #64
AaronP
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Default Re: Slow AA text rendering in KDE

Sorry to take so long replying to this thread. We are aware of this issue and will investigate ways to improve performance of subpixel-AA in future drivers.
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Old 04-03-06, 10:14 PM   #65
d13f00l
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Default Re: Slow AA text rendering in KDE

Quote:
Originally Posted by Linuxhippy
It could be that moden nvidia cards use shaders for subpixel-aa rendering so this description only applies to cards which do the subpixel-stuff in software like (i am quite sure) my NV18.
Nope, even modern cards don't use shaders for AA rendering. I was talking to one of the devs about this, it would be a possibility, however.

I think, like you said earlier, the issue might be latency involved copying data from system ram to the video card's ram over the AGP bus repeatedly.

For example, I was programming a game before. Drawing 1200 16x16 tiles to the screen was _MUCH_ _MUCH_ slower than drawing a single 640x480 surface to the screen.

If kwrite renders stuff character by character, this would result in each character being rendered in software in the system ram, than transported across the AGP bus back and fourth. That right there would kill performance, while rendering everything in software would be just mildly slow.

I've given up on the issue, this issue, among other performance issues, won't be _totally_ resolved until X moves away from software rendering and accelerates everything in hardware

However, any hacks nvidia could do to improve the situation in the meantime would be _MUCH_ appreciated.



The KDE team seemingly refuses to look at the issue. The latest bug I had posted there was closed a couple days ago, and most of the devs say they won't bother if it's fixed in KDE/QT 4. Sad panda

All we can do is wait for the issue to resolve itself through coincidence, or through direct efforts of Nvidia although I'm curious as to how much they can speed it up, especially on older cards without freely available math coprocessors(shaders) to offload the work to.

Last edited by d13f00l; 04-03-06 at 10:25 PM.
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Old 04-04-06, 06:07 AM   #66
Linuxhippy
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Default Re: Slow AA text rendering in KDE

Quote:
Originally Posted by d13f00l
Nope, even modern cards don't use shaders for AA rendering. I was talking to one of the devs about this, it would be a possibility, however.
Yep I forgot. Seems you are Mr. 100% very impoartant undercoder agent nvidia developer contact.
Well at least java does this: http://bugs.sun.com/bugdatabase/view...bug_id=6274813


Quote:
For example, I was programming a game before. Drawing 1200 16x16 tiles to the screen was _MUCH_ _MUCH_ slower than drawing a single 640x480 surface to the screen.
Well of course blitting a single image to an surface is something mordern cards can do in a very efficient manner. I guess when drawing the 16x16 tiles actually the whole opcode-generation / locking / context-switch-operating-system stuff is way slower than the blitting itself. However this is not latency since when blitting images you actually don't need to wait.
Furthermore this does not explain why a NV43 based card is 3,5 times slower than an old NV18 card.

Quote:
The KDE team seemingly refuses to look at the issue....
I've given up on the issue, this issue, among other performance issues, won't be _totally_ resolved until X moves away from software rendering and accelerates everything in hardware
1.) If KDE application 1 performs bad with one NVidia card and very good with another one its in my eyes not KDEs nore the applications fault. Its simply a speed regression either in the chip or in the driver!

2.) Why X? I would recommend to get some ground knowledge before generating tons of traffic blaming other guys which are not involved into this problem at all. It has never been and will never be X's responsibility to accalerate anything - thats why drivers exist.

lg Clemens
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Old 04-04-06, 01:16 PM   #67
xorbe
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Default Re: Slow AA text rendering in KDE

I tried QT4, and it didn't help. I could post those number too, later. I switched to grey AA + RenderAccel, since that is really fast.
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Old 04-04-06, 11:16 PM   #68
d13f00l
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Default Re: Slow AA text rendering in KDE

Quote:
Originally Posted by Linuxhippy
1.) If KDE application 1 performs bad with one NVidia card and very good with another one its in my eyes not KDEs nore the applications fault. Its simply a speed regression either in the chip or in the driver!

2.) Why X? I would recommend to get some ground knowledge before generating tons of traffic blaming other guys which are not involved into this problem at all. It has never been and will never be X's responsibility to accalerate anything - thats why drivers exist.

lg Clemens
In regards to font acceleration, I was referring to the nvidia X driver. Right now, the driver does non grayscale font aa in software. Cool link. I can't wait till Mustang is stable, it's supposed to have a lot of work done in the GTK L&F for Swing as well, yum. Dolphin should be pretty interesting too.

1) Well, it's really not that case here, on my PC. What a strange issue.
My GF4MX440 works just as bad with the latest driver as my 6200 with font AA. And, like someone else said, KWrite seems to render each letter indivudually, while kedit buffers each line. I joined #kde-devel and brought it up there as well, the developer who was looking into it had a dual Xeon system, and the problem didn't affect him as his system is fast enough to compensate. Others had the issue, and it happens with other drivers as well. I have not tried that QT application on my GF4MX, I'm just judging by KWrite performance between my two cards. Renderaccell is enabled with both.

2) Why do you think Microsoft is coming out with Aero, and why does XGl exist? It's a pain in the arse for driver developers to write specific code for each OS to accelerate various 2d video functions, and it brings around a lot of room for error when it's not done right. We're going to see a shift in responsibility, and it's for the better. Rather than Nvidia focusing on accelerating functions X provides, they can concentrate more on optimizing their OGL/DX API implementations, which in effect would speed up everything. Not to mention, a single codebase in X for accelerating various functions(font accell, transparent windows) would work and be accelerated on basically any card that supports OGL. It will save everyone time and the hassle once complete.

Last edited by d13f00l; 04-04-06 at 11:33 PM.
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Old 04-05-06, 01:22 AM   #69
Linuxhippy
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Default Re: Slow AA text rendering in KDE

Quote:
Rather than Nvidia focusing on accelerating functions X provides, they can concentrate more on optimizing their OGL/DX API implementations, which in effect would speed up everything.
Well then your opinion differens from NVidia's which think that X in top of OpenGL is a bad idea. An OpenGL backend can never be optimized as agressive as an optimized 2d driver since there are far more corner-cases to take care of and a lot more layering.

lg Clemens

Last edited by Linuxhippy; 04-05-06 at 08:15 AM.
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Old 04-05-06, 11:43 AM   #70
Linuxhippy
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Default Re: Slow AA text rendering in KDE

Quote:
Originally Posted by AaronP
Sorry to take so long replying to this thread. We are aware of this issue and will investigate ways to improve performance of subpixel-AA in future drivers.
Good to hear, I hope you succeed...

Best wishes, lg Clemens
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Old 04-06-06, 12:04 AM   #71
mnightt
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Default Re: Slow AA text rendering in KDE

Hi all,

I was with this problem for at least 6 moths and today I just change some settings in my xorg.conf to solve then.

KDE 3.5.0
Xorg 6.8.1 and 7.0 (works with both)
Nvidia Driver 1.0-8178
Kernel 2.6.15.2

I'm runnig Gobolinux [1].

Follow my Xorg changes:

Code:
Section "Module"
       #Load  "dri"
EndSection

Section "Device"
	Option      "RandRRotation" "1"
        Option      "RenderAccel" "1"
	Option      "Coolbits" "1"
EndSection
I hope this help.

1. http://www.gobolinux.org/index.php?lang=en_US
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Old 04-06-06, 01:18 AM   #72
Linuxhippy
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Default Re: Slow AA text rendering in KDE

Quote:
Originally Posted by mnightt
Option "RenderAccel" "1"
Well I guess if it would be that easy there would not be that much rumor about it

lg Clemens
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