HD7970x2 One can run at full speed but 2 will only run at half speed

[linuxninja39]

OK, I'm hopping for a little help here. I have 2 cards installed in PCIe x16 slots. They seem to be running fine. With cgminer 2.11.3 I can run each individually at ~550Mhash/s. But if I run them both the individually only run ~250. Any ideas why this might be and how I'd go about fixing it?

Thanks in advance.

[Kinetic915]

I'm confused. you say you run them individually and get 550 ad that you run them both individually at 250.

[Kinetic915]

do you mean combined 550 and individually 250? Which is basically the same thing lol 

[ryancs9]

try setting powertune option in cgminer to 20

[linuxninja39]

Running one GPU nets a TOTAL of ~500. Running both nets a TOTAL of ~500, each only running at ~250. If I start out running just one it'll hit ~500. If I enable the second one, the first one will drop to ~250.

I haven't tried the powertune option yet.

[#Darren]

I haven't tried the powertune option yet.

Give it a go and let us know what happens 

[linuxninja39]

I haven't tried the powertune option yet.

Give it a go and let us know what happens 

No love, both still running at half speed

[rethaw]

I'm having a similar problem. To describe in a little more detail:

Fresh install of Ubuntu 12.04 with drivers from repo.

Built cgminer using 2.8 APP SDK.

Run cgminer with two cards: reports both cards hashing, however, only GPU0 heats up. Performance seems to be what a single card would do (3-400MHash/s).

Run with a single device and get same performance as with 2.

To add to my confusion I ran GPU0 with -d 0 and got expected performance. I then ran another instance of cgminer with -d 1. The first instance dropped its hashrate in half and the second showed the same. Even when forcing the second device, the first device works!

This is a clean install, and I've tried variations on the cards being used with the same results.

[linuxninja39]

Yeah, I'm running a fresh install of Ubuntu 12.10, drivers from repo. I'm going to try installing ArchLinux with drivers from AMD. Also, do you have your CrossFire cable installed? I've tried with and without, no change.

[rethaw]

I had success building the 13.1 drivers myself and install APP SDK 2.7.

[linuxninja39]

I had success building the 13.1 drivers myself and install APP SDK 2.7.

Thats great, thanks for the follow up.

Yeah, it must be the repo drivers with ubunu. I re-imaged my box to an ArchLinux system and installed the drivers from Vi0L0. That did the trick. Now I'm getting 1.22Gh/s from the two cards. I'm now going to play with clock speeds and voltage to see if I can get a bit more out of em.