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What's going on? Memory bandwidth drops when FSB raised. (nF4 Ultra-D)


Metalex
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OK, after making sure my rig was totally Prime95 stable @ 2.4GHz (267x9, 5:6 divider), I thought I'd see what more I could get out of it.

 

I thought I'd try 2.45GHz (273x9, 5:6). It wasn't Prime stable at first - so I pushed RAM to 3.0v and CPU to 1.525v. All seemed well - I passed 6 hours or so on Prime - so I ran 3DMark2001, but only got 26.5K (I got 27K @ 2.4GHz!).

 

I ran the memory bandwidth test in Sandra, and found that the scores were 4500-5000MB/s @ 273FSB. I get around 6200MB/s @ 267FSB.

 

It's almost as if I'd switched 1T to 2T or something, but everything seemed fine.

 

Please can someone help me make sense of this?

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Drop you speed back to your "baseline" and re run your baseline (267x9, 5:6 divider). Maybe the data was recorded wrong, or maybe a mem setting really did change that you are not aware of? If you recorded all of your bios settings, then you can try to recreate each scenario again.

 

You may also try to run the benchmarks right after a reboot to help them be more consitant.

 

Just noticed you have a Tagan PSU. I think I remember reading about many issues with that brand of PSU and this DFi. You may want to look into that. So, check you voltages at all times while benching and make sure they stay the same at each FSB (except for VDimm of course).

 

Oh, make sure you plug in all power to the mobo....

 

Quad

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Yep, I've gone back to 267x9 and all is OK. I tried going back to 273 (and also 272 and 274) and the problem remained.

 

Like you suggested, I ran all my benches straight after reboot.

 

I'll have a look at the Tagan thing. I hope there isn't a problem.

 

All power connectors are in the board as well.

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OK, after making sure my rig was totally Prime95 stable @ 2.4GHz (267x9, 5:6 divider), I thought I'd see what more I could get out of it.

 

I thought I'd try 2.45GHz (273x9, 5:6). It wasn't Prime stable at first - so I pushed RAM to 3.0v and CPU to 1.525v. All seemed well - I passed 6 hours or so on Prime - so I ran 3DMark2001, but only got 26.5K (I got 27K @ 2.4GHz!).

 

I ran the memory bandwidth test in Sandra, and found that the scores were 4500-5000MB/s @ 273FSB. I get around 6200MB/s @ 267FSB.

 

It's almost as if I'd switched 1T to 2T or something, but everything seemed fine.

 

Please can someone help me make sense of this?

 

maybe your LDT on auto switching from 5x to 4x to 3x? Or auto ram clock?

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@Metalex,

 

Can you post your bios settings? Are you using "Auto" for anything?

Here you go, this is what I tried:

 

Genie BIOS Settings:

 

FSB Bus Frequency - 273

LDT/FSB Frequency Ration - 3

LDT Bus Transfer Width - 16 down 16 up

CPU/FSB Frequency Ratio - 9

PCI eXpress Frequency - 100Mhz

 

CPU VID StartUp Value - Startup

 

CPU VID Control - 1.525v

CPU VID Special Control - Auto

LDT Voltage Control - 1.20v

Chip Set Voltage Control - 1.50v

DRAM Voltage Control - 3.00v

 

 

DRAM Configuration Settings:

 

DRAM Frequency Set - 166 (DRAM/FSB:5/06)

Command Per Clock (CPC) - Enable

CAS Latency Control (Tcl) - 2.0

RAS# to CAS# delay (Trcd) - 02

Min RAS# active time (Tras) - 06

Row precharge time (Trp) - 02

Row Cycle time (Trc) - 08

Row refresh cyc time (Trfc) - Auto

Row to Row delay (Trrd) - 02

Write recovery time (Twr) - 02

Write to Read delay (Twtr) - 02

Read to Write delay (Trwt) - 03

Refresh Period (Tref) - 3120

Write CAS Latency (Twcl) - Auto

DRAM Bank Interleave - Enabled

 

DQS Skew Control - Auto

DQS Skew Value - 0

DRAM Drive Strength - Auto

DRAM Data Drive Strength - Auto

Max Async Latency - Auto

DRAM Response Time - Fast

Read Preamble Time - Auto

IdleCycle Limit - 256 Cycles

Dynamic Counter - Disabled

R/W Queue Bypass - 16 x

Bypass Max - 07 x

32 Byte Granularity - Disable(4 Bursts)

 

These DRAM settings are the optimised defaults on the 6/18-2 BIOS, except that I manually set to 166, Tcl 2.0, Trcd 02, Tras 06, Trp 02, Trc 08 and DRAM Response Time - Fast.

 

The settings work fine @ 267 (5/06), 3x LDT, 9x multi, 1.5v CPU VID, 2.9vdimm.

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The performance drop. You know why?? Because you are using memory divider DDR166(5/06). Try to set the memory to DDR200 or DDR 180 (If your RAM cannot oc at DDR200) or anyting higher than DDR166. You can see there is performance gain. I have once using memory divider @ DDR180 @ 280MHz because my RAM's oc limit is 260MHz (1/01) and I could get 7120 at Sisoftsandra as compared to 260Mhz by not using memory divider. The score was only 68**. If possible, do not use memory divider in oc. Of course by using memory divider you could oc your RAM to achieve higher FSB if your RAM could not support memory in synt with the FSB

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The performance drop. You know why?? Because you are using memory divider DDR166(5/06). Try to set the memory to DDR200 or DDR 180 (If your RAM cannot oc at DDR200) or anyting higher than DDR166. You can see there is performance gain. I have once using memory divider @ DDR180 @ 280MHz because my RAM's oc limit is 260MHz (1/01) and I could get 7120 at Sisoftsandra as compared to 260Mhz by not using memory divider. The score was only 68**. If possible, do not use memory divider in oc. Of course by using memory divider you could oc your RAM to achieve higher FSB if your RAM could not support memory in synt with the FSB
I understand what you're saying, but that's not really my problem.

 

My question is - why do I suffer a large drop in memory bandwidth when I run 273x9, 5:6 RAM divider (223MHz), 2-2-6-2-Fast, 1.525v CPU VID, 3.0vdimm ?

 

If I run 267x9, 5:6 RAM divider (218.5MHz), 2-2-6-2-Fast, 1.500v CPU VID, 2.9vdimm, everything is fine.

 

Basically, I get higher performance when using the lower FSB. When using 273x9, everything appears to be OK (according to CPU-Z, Sandra, Clockgen etc.), but the memory bandwidth drops like a stone.

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Use A64 Tweaker to see how the BIOS is setting the Auto timings at each HTT. Possibly the timings are being set differently due to the increase in HTT. If so, use the timings from A64 Tweaker at the lower HTT and set them in the BIOS.

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Use A64 Tweaker to see how the BIOS is setting the Auto timings at each HTT. Possibly the timings are being set differently due to the increase in HTT. If so, use the timings from A64 Tweaker at the lower HTT and set them in the BIOS.

Nice idea, I'll give it a go.

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Use A64 Tweaker to see how the BIOS is setting the Auto timings at each HTT. Possibly the timings are being set differently due to the increase in HTT. If so, use the timings from A64 Tweaker at the lower HTT and set them in the BIOS.
I've just tried A64 Tweaker with 267x9 and 273x9, and everything's exactly the same. :confused:

 

This is beginning to do my head in!

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