mersenneforum.org  

Go Back   mersenneforum.org > Great Internet Mersenne Prime Search > Hardware

Reply
 
Thread Tools
Old 2012-05-13, 22:09   #1
Brain
 
Brain's Avatar
 
Dec 2009
Peine, Germany

331 Posts
Question Influence of PCI Express Lanes to GPU Computing

Hello,

does anybody have experiences with the influence of PCI Express lane count to GPU Computing? Especially with regard to CUDALucas but mfaktc too. All I found is this:

Quote:
Originally Posted by axn View Post
Improved memory should have a more pronounced impact on CUDALucas.
Quote:
Originally Posted by BigBrother View Post
Well, The Card is now inserted into a PCI-E 2.0 x16 slot, and my brain surgery skills allowed me to fix a bent pin on the CPU socket so my memory is back at dual channel again.

One instance of mfaktc is now taking +-70% GPU instead of the 74% I reported yesterday, and nVidia's Visual Profiler shows transfer rates of 6Gb/s instead of 3 Gb/s, but since the amount of data to transfer is relatively small, there's no earth-shattering improvement. I could run the same benchmark I did yesterday again if James would like me to do that.
I have to decide whether I put my second GPU next to the first (X8 = 8 Lanes but closer and hotter) or to the boards bottom (X4).

I could simply try but I would like not to reinvent the wheel. I'd love to use the X4 slot for thermal reasons.

My guess: CUDALucas is not very intensive regarding CPU to GPU transfers - mfaktc will use a bit more. Any concrete numbers would be brilliant.

Thanks, Brain

Last fiddled with by Brain on 2012-05-13 at 22:10 Reason: This thread should have been in the GPU section :-(
Brain is offline   Reply With Quote
Old 2012-05-13, 22:22   #2
TheJudger
 
TheJudger's Avatar
 
"Oliver"
Mar 2005
Germany

11·101 Posts
Default

For mfaktc you've to transfer approximately four bytes per FC (factor candidate). So when you're GPU is good for 250M FCs per second than you'll need 1GB/s of PCIe bandwidth. Ofcourse there is some overhead but I guess it is save to ignore the overhead.

Oliver
TheJudger is offline   Reply With Quote
Old 2012-05-14, 04:34   #3
Brain
 
Brain's Avatar
 
Dec 2009
Peine, Germany

331 Posts
Default PCI Express v3.0

Quote:
Originally Posted by TheJudger View Post
For mfaktc you've to transfer approximately four bytes per FC (factor candidate). So when you're GPU is good for 250M FCs per second than you'll need 1GB/s of PCIe bandwidth. Ofcourse there is some overhead but I guess it is save to ignore the overhead.

Oliver
Me happy to have PCI Express v3.0:
http://en.wikipedia.org/wiki/PCI_Express
Capacity Per lane (each direction):
  • v1.x: 250 MB/s (2.5 GT/s)
  • v2.x: 500 MB/s (5 GT/s)
  • v3.0: 1 GB/s (8 GT/s)
  • v4.0: 2 GB/s (16 GT/s)
16 lane slot (each direction):
  • v1.x: 4 GB/s (40 GT/s)
  • v2.x: 8 GB/s (80 GT/s)
  • v3.0: 16 GB/s (128 GT/s)
Brain is offline   Reply With Quote
Old 2012-05-14, 07:21   #4
henryzz
Just call me Henry
 
henryzz's Avatar
 
"David"
Sep 2007
Cambridge (GMT/BST)

10110111011012 Posts
Default

Makes me wonder what performance I would get if I put a pcie 2 card in my pcie1.1 slot. I discovered a while back that they work just at the slower speed.
henryzz is offline   Reply With Quote
Old 2012-05-14, 08:18   #5
Stef42
 
Feb 2012
the Netherlands

2×29 Posts
Default

I found that running mfaktc (GTX460) in PCI-E x1 mode made the performance about 1/2 of that in a PCI-e x16 slot.
Using the same card in x4 mode gave roughly the same performance as on x16.

Last fiddled with by Stef42 on 2012-05-14 at 08:18
Stef42 is offline   Reply With Quote
Old 2012-05-14, 09:04   #6
LaurV
Romulan Interpreter
 
LaurV's Avatar
 
Jun 2011
Thailand

25·5·59 Posts
Default

For me no difference on x8/x16 (PCIe 2.0). Have no x4 cards/slots.
LaurV is offline   Reply With Quote
Old 2012-05-15, 18:37   #7
henryzz
Just call me Henry
 
henryzz's Avatar
 
"David"
Sep 2007
Cambridge (GMT/BST)

5,869 Posts
Default

My 1.1 x16 slot should theoretically run at the same speed as a 2.0 x8 slot. Sounds like I have more than enough bandwidth for a GTX460.
henryzz is offline   Reply With Quote
Reply

Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
GPU Computing Cheat Sheet (a.k.a. GPU Computing Guide) Brain GPU Computing 20 2015-10-25 18:39
I'm losing faith in my influence... seba2122 Prime Sierpinski Project 2 2015-07-22 23:46
PCI Express 3.0 ATH GPU Computing 2 2011-07-08 13:34
AMD Phenom II cache influence kaeptn_kork Hardware 3 2009-06-10 22:32
The difference between P2P and distributed computing and grid computing GP2 Lounge 2 2003-12-03 14:13

All times are UTC. The time now is 04:34.

Sun May 9 04:34:39 UTC 2021 up 30 days, 23:15, 0 users, load averages: 1.16, 1.52, 1.71

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.

This forum has received and complied with 0 (zero) government requests for information.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation.
A copy of the license is included in the FAQ.