Prime95 performance suffers after installing GT 640
 

Two nights ago, I installed an Nvidia GeForce GT 640 by Zotac in an HP dx7500 Microtower PC. Ever since then, Prime95 LL per-iteration times have jumped from 0.075 and .067 seconds on the two cores, to 0.111 and 0.085 seconds.

I do not have anything (mfaktc or CUDALucas) running on the GPU.

The weird thing is that a few weeks ago I installed a Zotac GT [B]630[/B] on an identical dx7500, and Prime95 performance was virtually unaffected whether or not mfaktc was running there. The times there are comparable to what they were on the problem machine before installing the 640.

The only difference between the two boxes is that the one with the 630 is running Vista Business, while the 640 is on an XP system. Both are 32-bit systems.

Does anybody have an idea what might be going on?

Rodrigo

Check on your CPU clock rate and temperature with and without the new card. Perhaps the card is physically blocking airflow, forcing the CPU to slow down to not overheat.

Two good utilities for it are Speedfan and CPU-Z.

Could this be a power problem? What was your video before the
GTX 640? Even tho this board doesn't require a great deal, HP is
notorious for using power supplies that are marginal, at best.
The additional load may have dropped the available voltage to the CPU
to force it to throttle down, perhaps?

Thanks for the ideas. I just got back in, so I haven't tried any of the specific suggestions above, but I do have the CPUID Hardware Monitor on both machines, and this is what they say (all values are current, not min/max):

[U]dx7500 w/GT 630 GPU (while running mfaktc and Prime95)[/U]:
Voltages: [motherboard]
VIN0 1.66 V
VIN1 1.68 V
VIN2 1.66 V

Temperatures:
TMPIN0 44C
TMPIN1 45C
TMPIN2 62C

Fans:
FANIN0 1547 RPM
FANIN1 959 RPM

Intel Core2 Duo E7600
Temperatures:
Core #0 54C
Core #1 53C

NVIDIA GeForce GT 630
Voltages:
VIN0 1.10 V

Temperatures:
TMPIN0 80C

Fans PWM:
FANPWMIN 74%


[U]dx7500 w/GT 640 GPU (problem machine now running Prime95 only)[/U]:
Voltages: [motherboard]
VIN0 1.66 V
VIN1 1.69 V
VIN2 1.66 V

Temperatures:
TMPIN0 41C
TMPIN1 38C
TMPIN2 54C

Fans:
FANIN0 1516 RPM
FANIN1 947 RPM

Intel Core2 Duo E7600
Temperatures:
Core #0 48C
Core #1 48C

NVIDIA GeForce GT 630
Voltages:
VIN0 0.95 V

Temperatures:
TMPIN0 33C

Fans PWM:
FANPWMIN 30%


The CPU and GPU temperatures are lower on the problem machine, as is the [B]G[/B]PU voltage.

Hope this helps to pin down where the problem is.

Rodrigo

[QUOTE=tServo;334246]Could this be a power problem? What was your video before the
GTX 640? Even tho this board doesn't require a great deal, HP is
notorious for using power supplies that are marginal, at best.
The additional load may have dropped the available voltage to the CPU
to force it to throttle down, perhaps?[/QUOTE]

It came with integrated video, Intel Graphics Media Accelerator X4500HD.

According to the System Information Viewer, both cores are running at 3.06-3.08 GHz; the spec is 3.06 GHz.

Rodrigo

I like cpuid myself, and though the output you posted doesn't show the cpu voltage it doesn't matter. The core temps are in the 40s, and cpu throttling (on my cores) doesn't start until you hit 90. Heat is not an issue here.

tServo suggested maybe power issues, but I don't know. Makes more sense than heat if those temps are right, but still.

One of the most alarming things I see on that output is that both computers say they have 630s in them. Shouldn't one be reporting a 640? Maybe you just need to reinstall the drivers.

[QUOTE=Aramis Wyler;334272]I like cpuid myself, and though the output you posted doesn't show the cpu voltage it doesn't matter. The core temps are in the 40s, and cpu throttling (on my cores) doesn't start until you hit 90. Heat is not an issue here.

tServo suggested maybe power issues, but I don't know. Makes more sense than heat if those temps are right, but still.

One of the most alarming things I see on that output is that both computers say they have 630s in them. Shouldn't one be reporting a 640? Maybe you just need to reinstall the drivers.[/QUOTE]
Oh, sorry about that -- my typo. CPUID does say 640 on the problem machine, I was retyping everything.

FWIW, according to SIV the CPU voltage on that machine is 1.29 on each core. I could try installing SIV on the "good" machine and see how that value compares.

Rodrigo

[QUOTE=Aramis Wyler;334272]
tServo suggested maybe power issues, but I don't know. Makes more sense than heat if those temps are right, but still.
[/QUOTE]

Looking at the CPUID results, I would agree, Aramis. Also since they are
Core 2 Duos, their throttling isn't as sophisticated as newer CPUs.

I would also agree to look next at driver issues. Double check the bios
to make sure the on-board video is disabled. Check to make sure
that the proper driver is shown by the operating system.

OK, I've updated the Nvidia graphics driver to the current version for the 640, and confirmed that the onboard video is disabled in the BIOS.

Still getting the same performance hit on Prime95.

What to try next? According to the Task Manager, Prime95 accounts for 99% of CPU cycles, which is correct for this machine that's dedicated to GIMPS.

Rodrigo

Just curious, what is your PSU?