Opteron 146 overclock not as good with 4x512mb

[duragezic]

For some reason, since I put in an additional 512mb PC3200 stick, it seems that CPU does not overlock as well.

For instance, I just tried 8x300 (my HTT mult is 3x so as to keep it under 1000 Mhz) with the memory speed at DDR266 (133Mhz) which from what I have written down means the memory frequency will be the HTT freq * .66, which works out to 198 Mhz. Considering all 4 sticks are PC3200, this should not be a problem. Since they are mixed sticks of unknown timings, the timing is all set to Auto/slowest Tras, Trcd, etc. I am running the sticks at 2.7 V; default is 2.6 V I believe.

So at 2.4 Ghz, ~1.45 V, 198 Mhz memory freq, the computer doesn't POST. The screen goes black, and after about 5 seconds it POSTs with default settings (1.6Ghz, 100Mhz memory freq).

So I need to use the very lowest memory divider, which is DDR200 (100 MHz) which should be HTT * .50.

And it's not necessairly the CPU either. Right now I'm at 315 HTT x 8 = 2.52 GHz (unsure of stability, but just testing stuff right now), but in order to do this and not have the BIOS reset to default settings during post, I needed to use the mem divider so that my memory frequency is only HTT * .50 = 157 MHz.

I'm unsure of how much a 150 MHz memory clock matters vs. a ~200 MHz clock. I never cared in the past that I would only be at about 183 MHz, but getting down to 150 MHz seems pretty low. And my timings are slow, but that matters even less I believe.

What is weird is that for example if I run 260 HTT * 8 = 2.01 GHz, I can use a memory divider DDR300 (150 MHz) which is HTT * .75 = 195 MHz. So running the CPU at 2.01 GHz, the 4x512 PC3200 works fine at 195 MHz.

So it's some sort of combination of the 4 sticks of memory and the CPU I guess. When I had 3x512, I was able to run 2.4 GHz+ CPU freq with memory at 190+ MHz.

What gives?

 

[duragezic]

Nickel020 posted in another thread:
"I don't know about Intel, but on A64s 4x512MB will only run at 2T which nets a 2-5% performance loss IIRC and depending on the motherboard may only run at DDR333 if all modules are double-sided."

I was aware of the 2T, but not about the DDR333. That may be my problem, but when I drop the CPU clock to 2ghz, my memory will run right up to 200 MHz I believe (I'll double check this tonight).

 

[duragezic]

bump

 

[myocardia]

Originally posted by: duragezic
Nickel020 posted in another thread:
"I don't know about Intel, but on A64s 4x512MB will only run at 2T which nets a 2-5% performance loss IIRC and depending on the motherboard may only run at DDR333 if all modules are double-sided."

I was aware of the 2T, but not about the DDR333. That may be my problem, but when I drop the CPU clock to 2ghz, my memory will run right up to 200 MHz I believe (I'll double check this tonight).

That's true, to a point. It all depends on which core you have. For instance, IIRC, the E3 cores and before (D0 and CG were before) has to be run @ 2T and 166 Mhz, although it might only be the D0 and CG's. The E6 stepping also has to be run @2T, and like the dual-cores, can run 4 sticks @2T @200 Mhz. And the reason you were able to overclock better with 3 sticks is because you weren't running in dual channel then. Adding the 4th stick not only added the additional fourth stick's stress on the memory controller, it also added dual-channel, which is also harder on the memory controller.

 

[f4phantom2500]

Since it is running in dual channel, I think you should be able to get by with slower speeds. I don't know how it works with A64's, but back in the AXP days when NF2 was introduced dual channel showed no benefit because DDR400 (or even 333 if you didnt have a 400fsb processor) in single channel was lined up to give the AXP's the max amount of bandwidth they could support anyway. So, theoretically, you could run the memory 100MHz in dual channel mode and get the same amount of bandwidth as you would if you were running 200MHz single channel mode since the processor could only take it in at 200MHz anyway. I could be totally wrong here but I think this is how it works. If it's the same way with A64's then you'd only need to run it at half the FSB in dual channel to get the same effective bandwidth if it were FSB speed in single channel (memory bandwidth ~1/2 but your processor can only take it as fast as the FSB can give it). Does this make sense to you guys?

 

[myocardia]

Originally posted by: f4phantom2500
Since it is running in dual channel, I think you should be able to get by with slower speeds. I don't know how it works with A64's, but back in the AXP days when NF2 was introduced dual channel showed no benefit because DDR400 (or even 333 if you didnt have a 400fsb processor) in single channel was lined up to give the AXP's the max amount of bandwidth they could support anyway. So, theoretically, you could run the memory 100MHz in dual channel mode and get the same amount of bandwidth as you would if you were running 200MHz single channel mode since the processor could only take it in at 200MHz anyway. I could be totally wrong here but I think this is how it works. If it's the same way with A64's then you'd only need to run it at half the FSB in dual channel to get the same effective bandwidth if it were FSB speed in single channel (memory bandwidth ~1/2 but your processor can only take it as fast as the FSB can give it). Does this make sense to you guys?

Yeah, that makes sense, but it isn't the way it works with A64's. You lose some performance if you lower the RAM's speed or run single channel. Not alot, and definitely nowhere near what you lose in single channel according to AMD, but every little bit helps.

For instance, going from single to dual channel, you gain between 75 & 100 Mhz worth of performance, in some applications. In others, you gain almost nothing. But then again, any app that RAM bandwidth affects will lose a slight amount of performance from either running single channel or lowering your divider.

 

[duragezic]

Alright, thanks for the input.

Previously I ran:
With 3x512mb, slowest/default timings, 2T, single channel @ ~200 MHz.

Now:
With 4x512, same timings, 2T, dual channel @ ~166 MHz.

Taking out of the equation that I do have an extra 512mb of RAM which likely outweights everything else, say that dual-channel provides 30-40 more MHz worth on average, then dual-channel @ 166 MHz should be at least as good as single-channel @ 200 MHz?

Not that I really was out of memory with 1.5GB at all, even with BF2 but 2GB should help, especially in the future. Even from tests showing BF2 uses 1.1-1.2 GB, my XP only uses about 100-120 mb when I game.

When I figure out the max overclock of my CPU, I can play with HTT, mem divider, multiplier, etc to get as close as possible to the max mem freq I can run. In addition, I am limited to 3-4-4-10 or whatever is very slow, because of the 1 stick of OCZ in there. If there is any leeway on the OCZ stick (the rest are 2.5-...), tightening the timings would help regain a few % worth of performance from the slower frequency, perhaps.

Yeah, it doesn't seem always true that 4 sticks causes the max memory freq to be 166MHz (DDR333) since I can run stock CPU freq, 4x512 @ 200 MHz, but if I want any sort of decent overclock that is the case. I would say that the extra CPU speed and 512mb more ram in dual channel is far better. I'm unsure of what core rev I have. I have a picture of the stepping at home but it probably doesn't say what core rev it is. I would think an Opteron 146 from Jan '06 would be E6, no? I thought E4 was the older A64s like the 3000+ and 3200+.

 

[f4phantom2500]

I don't think in games dual channel really makes a difference if they're at 200MHz but since it's 166 dual channel I would think that, in the end, you wouldn't be affected much in a game by the speed of the ram or the fact that it's dual channel instead of single. Basically I think it would about balance out. As for the core rev just go download cpuz, it'll tell you.

 

[Makaveli]

Correct me if i'm wrong, but I was under the impression that the 4 stick forces DDR333 speed was corrected in the E revision. But 2t with 4 sticks still remains.

And yes using 4 sticks of memory will lower your overclock comparted to just 2 sticks. that is why its recommended to go with 2x1GB sticks and not 4x512 if you are overclocking.

 

[myocardia]

Originally posted by: Makaveli
Correct me if i'm wrong, but I was under the impression that the 4 stick forces DDR333 speed was corrected in the E revision. But 2t with 4 sticks still remains.

And yes using 4 sticks of memory will lower your overclock comparted to just 2 sticks. that is why its recommended to go with 2x1GB sticks and not 4x512 if you are overclocking.

Haha, I have a horrible memory. That's why I was saying "it might only be the D0 and CG cores" and "IIRC". I was hoping that someone with a better memory than I have would jump in. Of course, it doesn't really matter now, he's said that his will run @ 200 Mhz, as long as it's @ 2T command rate.