memorybandwidth

[Hozee]

Hi all, long time no post but i d'ont post so easely, eh...

I notice that de memmorycontroller of the X2 is much slower then that of the singlecore. I did a test with 4 other persones on a forum with a X2, with sandra 2007 and we al had, approximately, the same memmoryspeeds with the X2's. Now i will give an example of the big difference in bandwidth between a X2 4600+ and a 3000+ venice, both overklocked( but that is not the issue): CPU @2700mhz, memmory @ 245mhz, timings 2.5-3-3-8. Memorybandwidth with sandra 2007 with the X2: int. buff. : 6305mb/s, float buff. : 6280mb/s
With the 3000+ @ the very same speeds as the X2, sandra 2007: int. buff:6954mb/s, float: 6924mb/s
This is a big difference in bandwidthspeed.
Why, this big difference in bandwidth between a dual and single core? Someone who knows?

[Samuknow]

Not sure why...does it affect real world performance? Does the dual core make up for this deficit?

[Andrei80]

What were the FSB's for the 2 setups, again? Were they both @245x9?

[Hozee]

@ Samuknow: think so, yes, some programs profit a lot with extra bandwith, like video editing.

@Andrei80: for sure, both tested with the same specs.
Both: CPU 300mhz X 9, memmory 300 X 166mhz = 245 mhz timings 2.5-3-3-8 like i explaine in the TS.

[jnansley]

Originally Posted by Samuknow

Does the dual core make up for this deficit?

Literally, no, just like no CPU will make up for a Geforce4 card (but a Geforce7 will make up for a lot of CPU....) In fact, if this is a consistent thing, having less memory bandwidth to any one core could quite possibly decrease performance over a single core in single-threaded applications.

[Hozee]

Yep, i agree with that. And the X2 seems to lack bandwith in comparison with the singlecore. Is this a unprecedented hidden bug in the memorycontroller of the X2? It seems so. That is what i want to know.

[Samuknow]

I would also like to know. I am planning my next build (finally) and need to know if I shoul spend the extra for the x2 AM2 CPU...

[Hozee]

Originally Posted by Samuknow

I would also like to know. I am planning my next build (finally) and need to know if I shoul spend the extra for the x2 AM2 CPU...

For the information: i talk here about the socket 939 cpu. Do not know how the AM2 differs in bandwith with the soc.939. That is a complete other question. Sorry no offence.

Offtopic : But i can tell you this, if you own a AMD soc.939 rig it is not to advise to purchase a AM2, cos the overall systemspeed is to be neglected in comparision with the soc. 939 with fast ddr1 memory, taking into account the extra costs that you have to make. ( new mobo and new memory). But if you must upgrade then the Conroe is, for now, a far better alternative. Make your choice.

[Hozee]

It seems i hit a difficulte issue here, thanks all who applied to my question. But til now no comments of the profs, in this threat? But for sure it is not acceptable if AMD hide some negative information regarding the X2.
Maybe i ame wrong so i register to the AMD forum, wich til now give me an error wen i want to replay. Send them a e-mail back and i hope this issue wil be soon history so that i kan get a awnser to my question.

[cadaveca]

The bandwidth difference is due to the Xtra L2 cache, as well as teh Xtra cpu. the differences between these cores are something i have touched on in the past.

[Samuknow]

Well where...? And does it make a diff on the AM2 CPUs?

[cadaveca]

Of course it does. The cpu has more cache to serve, or the emmorycontrolelr has another core to serve. It's pretty basic, if you ask me. this is not a characteristic of memory controll, but of the cpu itself, IMHO.

[jnansley]

Originally Posted by cadaveca

The bandwidth difference is due to the Xtra L2 cache, as well as teh Xtra cpu. the differences between these cores are something i have touched on in the past.

I must have missed that. I did feel that there would be some extra overhead involved in keeping both caches fed and consistent, but I didn't want to jump out on a limb and say that was the problem for a fact

[Samuknow]

Originally Posted by cadaveca

Of course it does. The cpu has more cache to serve, or the emmorycontrolelr has another core to serve. It's pretty basic, if you ask me. this is not a characteristic of memory controll, but of the cpu itself, IMHO.

The reason I ask is I am planning on an AM2 build and I want to go dual core. Will the performance increase of a dual core outweigh the mem bandwith deficit?

[cadaveca]

Not at all. In fact, as cpu speed increases, bandwidth will increase...a sure sign that the controllers are not quite maxed out...in other words it ain't gonna really make a bit of difference...less than .1%, in real world uses. It was Gizmo that noticed from my numbers that the difference between a venice and a sandiego was a proportional difference between a manchester and a toledo...so it's definately the cache @ play here.

[Hozee]

Originally Posted by cadaveca

...so it's definately the cache @ play here.

The cache....mmh. Okay, but my singlecore 3000+ has also a cache of 512mb like my 4600+ X2 but the memory bandwith is much faster like i mentioned in the TS. So, kan you tell me if there is a difference in working between the cache of a dual or a single core.

[cadaveca]

uh, dualcore has 512k x2....that's 1mb. 3000+ has 512k...that's 512k. As the memorycontroller has 2 caches to feed, of course the bandwidth is going to be a bit lower. Once again, it's the cache.

[Hozee]

Thx cadaveca i think i understand it now. So it means, for example, that a X2 with 2 X 1mb cache has a slower memorybandwith than one with 2 X 512mb, working of course @ the same speed.

[cadaveca]

yes...but it does not affect performance...it's merely an effect that is noticed due to the low-latency of the memory control...not really noticibly slower, but it DOES take longer for the info to go from cpu to mem as it passes through a larger cache.

[Hozee]

Thx cadaveca, it is clear now. It was a real headcracker for me but now i know for sure. I asked the same question in other forums but never get the right awnser, til now.
I had almost ask for an RMA, thinking that something was wrong with the memorycontroller cos i expected that de bandwith of an X2 was equal to the singlecore
And yes like you notice already, the performance of the X2 is bigger in comparision with my singlecore even with less bandwith. I notice that with the game F.E.A.R, a higher framerate with the same settings as my 3000+.
Thx again.