Go Back   nV News Forums > Linux Support Forums > NVIDIA Linux

Newegg Daily Deals

Reply
 
Thread Tools
Old 02-06-11, 04:00 PM   #1
jma
Registered User
 
Join Date: Oct 2009
Location: Stockholm
Posts: 33
Default Status of RT-patch?

What is the current status of the nvidia module regarding the RT-patch? Will it support patch-2.6.33.7.2-rt30?

Could we have a sticky or some mentioning about this somewhere?
jma is offline   Reply With Quote
Old 02-08-11, 06:52 AM   #2
coin-op-console
Registered User
 
coin-op-console's Avatar
 
Join Date: Jan 2011
Posts: 18
Default Re: Status of RT-patch?

The 256.52 driver from this ppa:

https://launchpad.net/~falk-t-j/+archive/lucid

Works very well with the 2.6.33-6-rt kernel once published in this ppa:

https://launchpad.net/~bojo42/+archive/rt/+packages

I've no knowledge on the 2.6.33-7-rt status though. My setup for realtime audio is:

2.6.38-rc2-lowlatency kernel, nvidia 270 beta drivers. No problems and extra xruns so far.
I hope I've been of some help. Cheers!
coin-op-console is offline   Reply With Quote
Old 02-08-11, 10:31 AM   #3
zander
NVIDIA Corporation
 
zander's Avatar
 
Join Date: Aug 2002
Posts: 3,740
Default Re: Status of RT-patch?

On a related note: although NVIDIA does not currently support real-time kernels, I can offer some related advice.

If your application is latency-sensitive (which it presumably is), then you may want to load the NVIDIA kernel module with the NVreg_UpdateMemoryTypes kernel module parameter set to 0 in future driver releases. This will force the driver to use write-back cacheable system memory allocations only, and avoid heavy-weight cache flushes at allocation time. The option is accepted by shipping drivers, but due to a missing optimization, they perform the offending cache flushes anyway. I can provide a patch, if you're interested. You may also want to request use of the highest p-state via the control panel.

I've used a combination of these two settings with good success using 195.36.xx at home (on a system controlling a high-precision CNC router via emc2).
zander is offline   Reply With Quote
Old 02-08-11, 11:37 AM   #4
jma
Registered User
 
Join Date: Oct 2009
Location: Stockholm
Posts: 33
Default Re: Status of RT-patch?

coin-op-console,

You've installed nvidia 270 beta on 2.6.38-rc2-lowlatency kernel (which I did not know even existed) without any patching or hand holding? That sounds promising.


zander,

I am currently on 195.36.15 - will the NVreg_UpdateMemoryTypes option work with that one and where do I put it?
jma is offline   Reply With Quote
Old 02-08-11, 01:00 PM   #5
zander
NVIDIA Corporation
 
zander's Avatar
 
Join Date: Aug 2002
Posts: 3,740
Default Re: Status of RT-patch?

The option works, but doesn't prevent the cache flushes. You can apply the attached patch to fix that problem, though. As to parameter placement, you have two options: you can either edit the nv-reg.h header file and change the default value of the parameter, or you can pass the option on at `modprobe` time. In the latter case, you can either pass it on the command line or via the appropriate modprobe.conf or modprobe.d/*.conf configuration file.
Attached Files
File Type: txt NVIDIA_kernel-195.36.15-8748438.diff.txt (1.2 KB, 87 views)
zander is offline   Reply With Quote
Old 02-08-11, 01:44 PM   #6
jma
Registered User
 
Join Date: Oct 2009
Location: Stockholm
Posts: 33
Default Re: Status of RT-patch?

zander,

There is one more instance of nv_flush_caches() in line 683 which is not tested like the rest - is this an oversight?


edit: Oh, that one was for kernel 2.4 ...
jma is offline   Reply With Quote
Old 02-08-11, 02:09 PM   #7
coin-op-console
Registered User
 
coin-op-console's Avatar
 
Join Date: Jan 2011
Posts: 18
Default Re: Status of RT-patch?

Quote:
Originally Posted by jma
You've installed nvidia 270 beta on 2.6.38-rc2-lowlatency kernel (which I did not know even existed) without any patching or hand holding?
Yes, thats right. Actually the lowlatency kernel doesn't include Ingo Molnar's realtime preemption patch. Its a vanilla kernel stack with some configurations aggressively tweaked.

Before the 2.6.38 kernels, lowlatency patched kernels were no way near the performance of rt kernels in terms of low latency audio dsp. But probably with this patch in the 2.6.38 stack:

http://www.phoronix.com/scan.php?pag...37_video&num=1

The situation has dramatically changed. I can't speak about realtime applications other than audio dsp though.
coin-op-console is offline   Reply With Quote
Old 02-08-11, 02:28 PM   #8
jma
Registered User
 
Join Date: Oct 2009
Location: Stockholm
Posts: 33
Default Re: Status of RT-patch?

coin-op-console,

What kind of buffer sizes are you talking about? I have a midi keyboard attached, so preferably I'd rather not go above 1 ms/buffer and not have more than two.
jma is offline   Reply With Quote

Old 02-08-11, 02:31 PM   #9
zander
NVIDIA Corporation
 
zander's Avatar
 
Join Date: Aug 2002
Posts: 3,740
Default Re: Status of RT-patch?

Quote:
Originally Posted by jma View Post
zander,

There is one more instance of nv_flush_caches() in line 683 which is not tested like the rest - is this an oversight?


edit: Oh, that one was for kernel 2.4 ...
Right, this path is specific to a workaround for broken 2.4 kernels (such as RHEL3's). It is not taken on any current kernel.
zander is offline   Reply With Quote
Old 02-08-11, 05:09 PM   #10
jma
Registered User
 
Join Date: Oct 2009
Location: Stockholm
Posts: 33
Default Re: Status of RT-patch?

I went for editing the default in nv-reg.h:

NV_DEFINE_REG_ENTRY(__NV_UPDATE_MEMORY_TYPES, ~0);

.. and changes that to zero - which was definitely not good. When X kicked in, my (VGA) monitor went blank and the machine died.
jma is offline   Reply With Quote
Old 02-08-11, 08:43 PM   #11
ledoc
Registered User
 
Join Date: Jan 2008
Posts: 330
Default Re: Status of RT-patch?

FWIW, if RT is more important than 3D, running nouveau could be an alternative.
ledoc is offline   Reply With Quote
Old 02-08-11, 11:48 PM   #12
jma
Registered User
 
Join Date: Oct 2009
Location: Stockholm
Posts: 33
Default Re: Status of RT-patch?

Quote:
Originally Posted by ledoc View Post
FWIW, if RT is more important than 3D, running nouveau could be an alternative.
Not realistically.

I am tapping the card (a GT220) for 80 Gflops of low latency RT audio processing using CUDA. This with 2 x 64 frames at 96 kHz*, __threadsync on every frame and a global barrier every 16 frames (which is about 90% of what is physically possible for the given set of algorithms.) The main processor, an E1200, only does interrupts and I/O and would have otherwise saturated at 20Gflops - at most. So no to Nouveau.

On the console I can then have a video feed on top of that as well, but in X, unfortunately, I can hardly draw a single pixel without xruns. Ironically, an unaccelerated Atari ST emulation in X works better/more predictably than X itself.**

What zander says below has some positive effect in so far that as long as I do not rock the boat, I can now have the same performance in X as on the console. All desktop toys like clock and cpu/network monitoring must be turned off though.

* In comparison with JACK Audio latency, add one buffer because one is in transit back and forth to the GPU.

**with threads reduced by 25% to 192 and 3 x 96 frame buffers, the Atari ST emulation runs stable 800x600 fullscreen, 5 times "overclocked" - this is snappy! - whereas the much smaller "Adjust Date & Time" window in gnome causes xruns each and every second.
jma is offline   Reply With Quote
Reply


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -5. The time now is 07:24 AM.


Powered by vBulletin® Version 3.7.1
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright 1998 - 2014, nV News.