bandwidth disparity

[mk17]

Hi everyone. I have a quick question regarding memory bandwidth:





On int buffered my machine runs between 20-30% faster than the comparisons. But for float buffered tests my machine sinks to about 20-25% of comparisons.

Running Corsair [email protected], 4:5 (800MHz)@5-5-5-15.
[email protected]. MCH @1.53v. Abit AW9D-MAX.

MemTest runs happily for hours. But something seems badly wrong with the Bandwith Efficiency falling to 8% for float.

Has anyone any ideas? Does this look like a voltage issue? Or is my ram hosed?

 

[Firegod]

Running a ratio wouldn't have anything to do with it, perhaps? I'm not sure really...

I know on my DFI board (for example) there are lots and lots of memory options to alter which either effect bandwith efficiency or stability (i.e. a trade-off). Perhaps some settings on your board are configured incorrectly (or running "default" values) causing poor bandwidth results?

When I was first setting my system up, this was my initial result for bandwith (new result after tweaking are in red):-

Int Buff'd iSSE2 (Integer STREAM) Results Breakdown
Assignment : 6841MB/s [COLOR=Red]7512MB/s[/COLOR]
Scaling : 6830MB/s [COLOR=Red]7521MB/s[/COLOR]
Addition : 6690MB/s [COLOR=Red]7300MB/s[/COLOR]
Triad : 6692MB/s [COLOR=Red]7296MB/s[/COLOR]
Data Item Size : 16 byte(s)
Buffering Used : Yes
Offset Displacement Used : Yes
Bandwidth Efficiency : 93% (estimated) [COLOR=Red]84% (estimated)[/COLOR]

Float Buff'd iSSE2 (Float STREAM) Results Breakdown
Assignment : 6853MB/s [COLOR=Red]7509MB/s[/COLOR]
Scaling : 6838MB/s [COLOR=Red]7518MB/s[/COLOR]
Addition : 6613MB/s [COLOR=Red]7161MB/s[/COLOR]
Triad : 6558MB/s [COLOR=Red]7101MB/s[/COLOR]
Data Item Size : 16 byte(s)
Buffering Used : Yes
Offset Displacement Used : Yes
Bandwidth Efficiency : 92% (estimated) [COLOR=Red]83% (estimated)[/COLOR]

As you can see, I received more bandwidth yet efficiency dropped by around 10%.

EDIT: Just noticed, your FLOAT results are only in the hundreds!

 

[Jokester]

Have you tried rerunning them at stock speeds? Might be an instability issue.

Jokester

 

[mk17]

Thanks for the responses guys.

Everything reset to default (cpu, ram volts, mch, etc.):


Defaults plus a bump for Ram V, and MCH:



Stock speeds seem to indicate that the ram doesn't like 1.80v very much. However this doesn't explain the poor float performance.

Anyone got any ideas? Should the MCH be pushed further, i.e. ram @ 2.1, mch @ 1.6?

 

[mk17]

found it:




Turned out to be an AW9D mobo issue. I downloaded a beta of bios v13, problem solved. I haven't tweaked it for performance just yet, its not as stable as 12 was, but it has unlocked the multi to go higher than 11 (31x I think).

 

[Firegod]

Nice one.