Ivy Bridge and PCIe 3.0

[1337n00b]

I just read that the Ivy bridge CPU will "support" PCIe 3.0. I didn't know the CPU could cap how much bandwidth a video card bus could utilize, so I must be missing something?

If not, would the Sandy Bridge CPU cap a PCIe 3.0 motherboard and video card from utilizing the extra bandwidth?

 

[RobDickinson]

The PCIe controller chip is on the CPU itself.

A SNB chip in a pcie 3.0 board will still be pcie 2.0

 

[Mark R]

Sandy Bridge CPUs have PCIe v2.0 ports on them.

If you plug in a very new graphics card which has a PCIe v3.0 connector, then the SB CPU will ask the graphics card to slow down to PCIe v2.0 speed. It's exactly the same as if you plugged an old graphics card with PCIe 1.0 connectors, it would ask the CPU to slow down to PCIe 1.0 speed.

A SB motherboard wouldn't have PCIe 3.0 slots on it, since the PCIe circuits are on the SB chip itself. The job of the motherboard is simply to have some PCIe slots, and run wires from the slots to the SB CPU.

 

[1337n00b]

I got ya. I'm still running a P4 with AGP. Really outdated.

 

[RussianSensation]

Don't worry about it. By the time videocards exceed the bandwidth of PCIe 2.0 16x, Sandy Bridge and Ivy Bridge will be ancient history as far as adequate performance is concerned. Even now PCIe 2.0 8x only results in a 2% performance penalty vs. PCIe 2.0 16x.

 

[1337n00b]

Don't worry about it. By the time videocards exceed the bandwidth of PCIe 2.0 16x, Sandy Bridge and Ivy Bridge will be ancient history as far as adequate performance is concerned. Even now PCIe 2.0 8x only results in a 2% performance penalty vs. PCIe 2.0 16x.

Guessing their just setting the standard now, even though it will be a few years before the new slot bandwidth can actually be utilized?

 

[Rvenger]

Yeah, look how long it took to notice a difference in performance b/w DDR2 and DDR3.

 

[Borealis7]

forget PCIe 3.0 for graphics card...think PCIe SSDs!

 

[Edrick]

Don't worry about it. By the time videocards exceed the bandwidth of PCIe 2.0 16x, Sandy Bridge and Ivy Bridge will be ancient history as far as adequate performance is concerned. Even now PCIe 2.0 8x only results in a 2% performance penalty vs. PCIe 2.0 16x.

The real benefit of PCIe 3.0 will be that a user can SLI at 8x and 8x @ 3.0 speeds and not suffer any penalty. So in reality, an IB CPU with 16 lanes of PCIe 3.0 will be very similar to a CPU with 32 lanes of PCIe 2.0.

 

[PreferLinux]

Or how about quad-SLI at 4x, 4x, 4x, 4x and have no penalty over what is currently done with 8x?

 

[RussianSensation]

The real benefit of PCIe 3.0 will be that a user can SLI at 8x and 8x @ 3.0 speeds and not suffer any penalty. So in reality, an IB CPU with 16 lanes of PCIe 3.0 will be very similar to a CPU with 32 lanes of PCIe 2.0.

I think the real benefit of faster PCIe is more bandwidth required for other devices (such SATA-Express, Thunderbolt/Lightpeak). The need for faster PCIe 3.0 for GPUs is not there at all.

 

[toyota]

they add those features now BEFORE you actually need them. the mobos people buy in 2011 are not all going to be in the dump in 2012 or 2013. sometimes mobos can be relevant for 4 or 5 years or more so having a mobo with features now that might be useful down the road makes sense.

 

[pantsaregood]

Yeah, the need for GPU bandwidth is actually amazingly low.

PCI-E 2.0 4x has the same bandwidth as AGP 8x did back in the early 2000s, yet a lot of cards can run in PCI-E 2.0 4x mode without a huge performance loss. When running multiple GPU setups in 16x/4x modes, the loss is very minor.

 

[Edrick]

Yeah, the need for GPU bandwidth is actually amazingly low.

PCI-E 2.0 4x has the same bandwidth as AGP 8x did back in the early 2000s, yet a lot of cards can run in PCI-E 2.0 4x mode without a huge performance loss. When running multiple GPU setups in 16x/4x modes, the loss is very minor.

Just because the need is "low" for now, does not mean it will stay that way in the next year(s).

 

[Rhezuss]

So is PCIe 3.0 would be a good argument to hold on buying a new mobo for a near future upgrade?

 

[xBiffx]

So just to make it clear. Can any board able to accept SB @ PCIe 2.0 accept IB @ PCIe 3.0?

 

[Arkadrel]

I just read that the Ivy bridge CPU will "support" PCIe 3.0. I didn't know the CPU could cap how much bandwidth a video card bus could utilize, so I must be missing something?

If not, would the Sandy Bridge CPU cap a PCIe 3.0 motherboard and video card from utilizing the extra bandwidth?

Do you use Crossfire/SLI with a few cards? I imagine thats wherer you ll see the biggest gains from PCIe 3.0.

I dont think a single card, currently is near reaching a bottleneck even on just PCIe 2.0
(or only very small amounts, see below 2%-7% differnce between x4 and x16).

With a Geforce 480.

I imagine that with faster cards (and CPU's), the issue will become more evident.
(ei. more than 2% jump from x8 -> x16).
(from x4 -> x16 is a 7% performance jump).

Which is where PCIe 3.0 will come in, to fix things.

 

[greenhawk]

So is PCIe 3.0 would be a good argument to hold on buying a new mobo for a near future upgrade?

not really. It might help, but only if something would take advantage of it before your next major upgrade.

Personally, not expect anything for the average user is going to need it for 3 or so years at best, if even then.

To me it is like USB3. It has been around for a few years and only now starting to show up on new systems as a standard feature. While important, it does not help most people as

a) USB 2 is fast enough for most tasks
b) file transfer loves the extra speed, but the machine you are transfering to proberly still only has USB2.

 

[greenhawk]

So just to make it clear. Can any board able to accept SB @ PCIe 2.0 accept IB @ PCIe 3.0?

No. The board needs a few extra parts that can run at the PCIe 3.0 speeds. Without it (at best), IB will run at 2.0 speeds. (assuming all other features IB needs are met.

I say at best as I do not think even intel has anounced what is needed to run IB on a current 1155 motherboard. It is all speculation at the moment. Not that it is stopping motherboard manufactures of releasing motherboards like Asrock's "Gen3" range which is ment to be fully IB ready.

edit: I should add also that some talk from intel is that they are allowing some FSB changes on some IB chips. A feature none of the current motherboards support as SB does not allow any changes to FSB. So even if the motherboard accepts PCIe 3.0, it might not fully support all features of a IB cpu.

Still to early to be 100%, but you can expect intel to allow IB to run (even if limited in some way) on current 1155 boards.