Civilization Beyond Earth - Hybrid CrossFire investigation

[AtenRa]

While i was preparing my APU Hybrid review, I came upon a strange behavior of the Civilization Beyond Earth Hybrid performance when both the APU and the dGPU were overclocked.

When both the APU and dGPU are operating at Default clocks in Hybrid Cross Fire mode, the performance is faster than when both are Overclocked at low resolutions of 1280x800 and 900p.

At first i though it was a throttling problem due to high temperatures. But even with a Water cooler on the APU and an extra fan above the motherboard VRMs the performance was the same as before, sub par against the default clocked Hybrid CrossFire.

Sustem hardware and steup

APU : AMD A10-7850K
Motherboard : ASUS A88XM-Plus
Memory : 2x 4GB 2133MHz Kingston Genesis 11-12-11 1.65V
HDD : Seagate Barracuda ST1000DM003 1TB SATA-6
PSU : Thermal Take TR2 380W 80plus Bronze

dGPU : GigaByte GV-R725OC-2GI (R7 250 2GB DDR-3)
GPU clock @ 720MHz
GPU Mem @ 800MHz

Second dGPU for reference at 1080p Medium settings
Gigabyte HD7790 1GB GDDR-5 OC
GPU Core @ 1075MHz (R7 260X is at 1100MHz)
Memory @ 1500MHz (same as R7 260X)

AMD Catalyst 14:12 Omega
Windows 8.1 64bit

Overclocking APU
CPU Core @ 4.35GHz
iGPU @ 856MHz
DDR-3 @ 2424MH 11-13-13


Overclocking R7 250
GPU @ 855MHz
DDR-3 @ 830MHz

For the review I have used the in-game benchmark with Mantle (except for the HD4600).

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At 1280x800 Hybrid Cross Fire scaling vs A10-7850K iGPU = 83,44%
As you can see from the graph, when Overclocked in Hybrid Cross Fire mode the results are inferior than at default clocks.
Overclocked TimeFrames are worst as well if you compare them against the Hybrid Cross Fire at default clocks.

A10-7850K iGPU with Mantle

 

[AtenRa]

I dont know why but at 1600x800 Hybrid Cross Fire scaling vs A10-7850K iGPU is more than 100%, reaching 105,90%

 

[AtenRa]

At 1080p Low settings, Hybrid Cross Fire performance is higher when OCed but minimum fps are lower than when at default clocks.

Also, Hybrid Cross Fire Scaling is very low at only 33,33%. At 1080p perhaps there is a Memory Bandwidth bottleneck.

 

[AtenRa]

This is the only time that when both the APU and the R7 250 are overclocked, they are performing faster both at minimum and average fps than against the default clocked Hybrid Cross Fire.
The Hybrid Cross Fire scaling vs the A10-7850K is 58,89%.
The HD7790 is faster and with better frametimes than the Hybrid Cross Fire at 1080p with Medium settings. Also worth mentioning that A10-7850K paired with the HD7790 is not only faster than the Overclocked Hybrid Cross Fire but it uses less power as well.

 

[Erenhardt]

My bet is OCed CPU is taking some of the power budget from igp. You would have to monitor IGP usage% and clocks through the runs to determine if that is the case.

Try lowering CPU OC a bit and leave IGP clocks as is, or even bit higher.

Check what have an impact on the scaling - CPU or IGP clocks.

 

[AtenRa]

My bet is OCed CPU is taking some of the power budget from igp. You would have to monitor IGP usage% and clocks through the runs to determine if that is the case.

Try lowering CPU OC a bit and leave IGP clocks as is, or even bit higher.

Check what have an impact on the scaling - CPU or IGP clocks.

yea i was thinking something like that, i will investigate by lowering the CPU overclock.

 

[zagitta]

I remember seeing a thread here ages ago about someone with a similar issue when overclocking their APU and using OpenCL. I think it had something todo with a cache clock getting locked lower than normal when OC'ed which seemed to be a driver bug but don't quote me on it.

I tried searching a bit for the thread but was sadly unable to find it.