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AMD Kaveri Refresh A10-7870K Apu arrives. - Page 41

post #401 of 532
DDR4 would bring no performance improvement for Steamroller, only even worse latency.
Carrizo supports DDR4, but it doesn´t improve the performance at all since the memory controller doesn´t support higher frequencies than DDR-2400.

In dual channel DDR4 cannot solve the bandwidth issue of the APUs as it will never be able to reach high enough clocks. Steamroller APUs already would require ~96GB/s in order to get the maximum performance out of the GPU.

That´s GDDR5/X or HBM territory.
post #402 of 532
Quote:
Originally Posted by The Stilt View Post

DDR4 would bring no performance improvement for Steamroller, only even worse latency.
Carrizo supports DDR4, but it doesn´t improve the performance at all since the memory controller doesn´t support higher frequencies than DDR-2400.

In dual channel DDR4 cannot solve the bandwidth issue of the APUs as it will never be able to reach high enough clocks. Steamroller APUs already would require ~96GB/s in order to get the maximum performance out of the GPU.

That´s GDDR5/X or HBM territory.

Quad-channel can't even touch that. It's why I think DDR generation is dead. We need 3D or 2.5D system ram. It's denser and faster.
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post #403 of 532
Thread Starter 

Rather than worrying about what we can't get for $150, why not have a go at exploring what we can?

 

For all the moaning about the 2400MHz IMC limit there is a memory frequency record over on HWBOT of 2900MHz for the A10-7870K, which - together with my own results over 2600MHz - shows there is more there than just an OC ceiling.

And we can talk about bottlenecking but even before anyone starts exploring DX12 for anything other than i7/Singularity high jinks we should bear in mind that in OpenCL even the mighty R9 Fury X gets a 17% performance increase when it duals with the A10-7870K's iGpu.
 

post #404 of 532
Ordered my 7870K Today. Time to take a look at Dual graphics smile.gif.
Edited by -Leopold- - 11/1/15 at 11:21pm
    
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post #405 of 532
Quote:
Originally Posted by Himo5 View Post

For all the moaning about the 2400MHz IMC limit there is a memory frequency record over on HWBOT of 2900MHz for the A10-7870K, which - together with my own results over 2600MHz - shows there is more there than just an OC ceiling. 

Yeah but is that DDR3-2900 system stable? I've gotten DDR3-2640 stable before, and DDR3-2538 or . . . whatever it was, but my NB would not max out under those circumstances. So I had to pick 2100 MHz NB and DDR3-2400 or ~1.9 GHz NB and DDR3-2538 or 2640. Higher RAM speeds were good for somethings, but not so good for others when taking into account the NB speed penalty.

For CPU-heavy stuff, higher NB speed was better.
post #406 of 532
Quote:
Originally Posted by Himo5 View Post

Rather than worrying about what we can't get for $150, why not have a go at exploring what we can?

For all the moaning about the 2400MHz IMC limit there is a memory frequency record over on HWBOT of 2900MHz for the A10-7870K, which - together with my own results over 2600MHz - shows there is more there than just an OC ceiling.


And we can talk about bottlenecking but even before anyone starts exploring DX12 for anything other than i7/Singularity high jinks we should bear in mind that in OpenCL even the mighty R9 Fury X gets a 17% performance increase when it duals with the A10-7870K's iGpu.

rolleyessmileyanim.gif

The same way you could say that FXs can do 8.7GHz+ since someone has managed to take a screenshot at that frequency.

Steamroller or Excavator based designs CANNOT operate properly at frequencies higher than 2400MHz. One of the reasons why the memory controller in Carrizo / Bristol Ridge is restricted to 2400MHz, even it supports DDR4. You can configure the DRAM Phy to output other frequencies (e.g. 2666, 2800, 2933, 3000, 3200), however it cannot operate stable at those speeds. AMD has validated the IMC in Steamroller at 2133MHz, which is already higher than the outsourced IP was originally designed to operate.

The IMC might be able to operate slightly higher than that without causing severe issues, but not without sacrificing the reliability and stability or without violating the electrical specifications (both signals and voltage levels). "Results" with sub-zero cooling, >1.625V DRAM VDD, >1.32V VDDNB or underclocked NB or GFX or single channel / half populated ranks don´t count either.

But obviously you know this stuff much better than I or AMD / Altera engineers do thumb.gif
post #407 of 532
Thread Starter 
Quote:
Originally Posted by The Stilt View Post


rolleyessmileyanim.gif

The same way you could say that FXs can do 8.7GHz+ since someone has managed to take a screenshot at that frequency.

Steamroller or Excavator based designs CANNOT operate properly at frequencies higher than 2400MHz. One of the reasons why the memory controller in Carrizo / Bristol Ridge is restricted to 2400MHz, even it supports DDR4. You can configure the DRAM Phy to output other frequencies (e.g. 2666, 2800, 2933, 3000, 3200), however it cannot operate stable at those speeds. AMD has validated the IMC in Steamroller at 2133MHz, which is already higher than the outsourced IP was originally designed to operate.

The IMC might be able to operate slightly higher than that without causing severe issues, but not without sacrificing the reliability and stability or without violating the electrical specifications (both signals and voltage levels). "Results" with sub-zero cooling, >1.625V DRAM VDD, >1.32V VDDNB or underclocked NB or GFX or single channel / half populated ranks don´t count either.

But obviously you know this stuff much better than I or AMD / Altera engineers do thumb.gif

 

All I am saying is what you have said yourself in the past - that memory could operate at higher frequencies than 2400MHz.

 

You now talk about instability which I haven't found in these very areas 2400-2520MHz where you suggested we look. The fact that someone on HWBOT could run memory at 2900MHz shows there is capacity above 2400MHz.

 

I don't know why you are now trying to impose this 2400MHz ceiling unless you can show evidence of memory degradation at these higher speeds.

post #408 of 532
Can anybody recommend a Single Slot R7 250 for Dual Graphics? Better go with 1GB DDR5 or 2GB DDR3?
    
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post #409 of 532
Quote:
Originally Posted by The Stilt View Post

rolleyessmileyanim.gif

The same way you could say that FXs can do 8.7GHz+ since someone has managed to take a screenshot at that frequency.

Steamroller or Excavator based designs CANNOT operate properly at frequencies higher than 2400MHz. One of the reasons why the memory controller in Carrizo / Bristol Ridge is restricted to 2400MHz, even it supports DDR4. You can configure the DRAM Phy to output other frequencies (e.g. 2666, 2800, 2933, 3000, 3200), however it cannot operate stable at those speeds. AMD has validated the IMC in Steamroller at 2133MHz, which is already higher than the outsourced IP was originally designed to operate.

The IMC might be able to operate slightly higher than that without causing severe issues, but not without sacrificing the reliability and stability or without violating the electrical specifications (both signals and voltage levels). "Results" with sub-zero cooling, >1.625V DRAM VDD, >1.32V VDDNB or underclocked NB or GFX or single channel / half populated ranks don´t count either.

But obviously you know this stuff much better than I or AMD / Altera engineers do thumb.gif

I hope, Zen FX IMC will be stronger, Intel is today easy at over 3200 MHz DDR4with Skylake. Last jump were with 15h up to 2500 MHz ddr3 effective in 2011.
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post #410 of 532
Did Altera design the IMCs for Kaveri and Carrizo?
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