Topic: New rig problem: direct pcie 16x connection is slower than 1x riser - page 2. (Read 3233 times)

(also posted on reddit/r/litecoinmining, but maybe you guys have a solution for me)

Hello fellow miners.  I built my rig two days ago and noticed a persistent problem.  I have three R9 290 cards, two from powercolor, one from xfx.  The two powercolor cards are plugged directly into the pcie 16x slots, and the xfx is in a 1x riser.  For some reason, I get 80-100 kH/s higher rates on the card in the 1x riser.  I tried switching the xfx card and one of the powercolors, and I get the same results, so it's not from differences in the cards. 

I'm using cgminer 3.7.2 on Windows 7 x64 with Catalyst driver 13.11 Beta9.5 and no extra app sdk installed.  I've used many different configurations, all giving the same performance drops on the two direct pcie 16x cards.  Currently I'm using something similar to the rumorcity ["R9 290 and R9 290X – Sweet Spot"](http://rumorscity.com/2013/12/03/litecoin-gpu-mining-with-amd-r9-290-and-r9-290x-sweet-spot-for-1000khashsec/) article.  My launch batch also sets GPU_MAX_ALLOC_PERCENT 100 and GPU_USE_SYNC_OBJECTS 1 . 


Here is a screenshot showing the issue (GPU 2 is on the 1x riser):

https://i.imgur.com/nZTat60.png

My rig specs:

2x PowerColor AXR9 290 4GBD5-MDHG/OC Radeon R9 290 4G

1x XFX R9-290A-ENBC

mobo: MSI 970A-G46 AM3+ AMD 970 SATA 6Gb/s USB 3.0 ATX A

cpu: AMD Sempron 145 Sargas 2.8GHz Socket AM3 45W

ram: 8GB g.skill DDR3 1600 (4X 2GB)

psu: CORSAIR HX Series HX850 850W ATX12V 2.3 / EPS12V 2

hdd: some old seagate sata hard drive

I would appreciate any tips on how to get around this.  I'm kind of stumped as to why the direct pcie 16x ports are slowing down my hashrates... maybe the BIOS is clocking them down to save power?  I haven't seen any setting like this when looking though.  Is there some way that Windows 7 can slow the pcie bus?