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arcon

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#272153 11-Jun-2020 19:41
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In a month or so I will be in the market for a new PC for heavy GPU rendering & post production. I haven't bought a PC in 5 years & have some confusion around PCIe lanes... the new rig will have two RTX graphics cards and three M.2 drives. I understand the latter ideally need 4 lanes each... but Intel's new 10th gen CPU's only seem to support 16 lanes, enough for 1 graphics card...? I'm obviously missing something or have read something misleading lol. Any advice appreciated would be on what I should look out for or avoid purchasing etc.


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richms
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  #2503204 11-Jun-2020 19:47
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The rest of the lanes come from the chipset and are slower because they all share a single link to the CPU over some other stuff.

 

For more fast lanes from the CPU you have to look at the big workstation xeon chips or else hop over to team red where they dont seem to be as scared of putting good specs into consumer CPUs.





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arcon

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  #2503217 11-Jun-2020 20:00
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richms:

 

For more fast lanes from the CPU you have to look at the big workstation xeon chips or else hop over to team red

 

I'm guessing this means AMD haha. Yep I absolutely would consider it, I haven't had a chance to look in great detail yet, I think my initial concern was slightly slower single threaded performance which is a big deal when running any kind of simulation in Maya (my 3D app).


toejam316
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  #2503226 11-Jun-2020 20:31
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Can you push that month out further? Sometime in the next few months, AMD should be releasing Zen 3 parts, the Ryzen 4000 series processors. These should by all accounts outpace the current Intel parts, as the current (fairly strong) rumours are pointing to 15% IPC gains in some cases. You'd have more cores for a better price, more CPU lanes with support for PCI Gen 4 for faster IO, and I suspect probably around the same time the new Nvidia Ampere parts should hit market, and possibly the RDNA 2 parts if you want to go with an AMD GPU, too. Right now, only buy a desktop computer if you HAVE TO. There's the mantra of there's always something better around the corner, but there's a bunch of stuff due out this year, sooner rather than later.





Anything I say is the ramblings of an ill informed, opinionated so-and-so, and not representative of any of my past, present or future employers, and is also probably best disregarded.




arcon

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  #2503229 11-Jun-2020 20:59
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Yeah I can probably wait a few months. Can't buy AMD graphics - Redshift only runs on CUDA. Not much in FX work makes use of multiple cores... especially during dynamic sims or real-time playback. I've even seen a test that called into question turbo-boost in favour of CPUs with a higher base clock... maybe why my trusty i4790K at stock 4GHz has lasted so long lol.

 

I will check out what's around the corner from AMD though.


timmmay
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  #2503237 11-Jun-2020 21:23
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I'm waiting for Ryzen 4000 as well, though only because I'm not in a hurry. 2600K is working fine, problem is USB ports are wearing out.

 

Intel are way ahead with single thread performance. Probably not a lot of point waiting if you only care about that. For comparison of what I can find at PB Tech Ryzen 3950 is $1400 and gets 2750 score for a single thread, the i5 10500 costs $400 and gets a touch higher. Heck there's even an i3 that gets a higher score than all but the most expensive Ryzen. i7 7700 and 8700 are both higher than most Ryzen too. Your 4790 is only about 10% slower than that.

 

There's probably not a lot of point upgrading CPUs if single threaded is all your care about. You might get 20% better performance, could be a lot to spend for a minor gain.


arcon

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  #2503243 11-Jun-2020 21:56
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My current mobo only supports single M.2, and my PSU isn't ideal for dual graphics, so I figured a good excuse to get a new rig complete with cool new lighting that new mobos have :D I'm not sure the old PC would sell with a CPU missing if I transferred it, that's assuming they work in new mobos.

 

For interest I was checking out the Xeon-W2125... 4Ghz base clock, huge memory bandwidth and PCIe lanes for africa, but they don't seem to sell in NZ anyway.


  #2503309 12-Jun-2020 06:10
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your old cpu wont work in newer motherboards

 

intel only supports about 2 generations of CPU per motherboard series. AMD is a little more forgiving


 
 
 

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zenourn
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  #2503315 12-Jun-2020 06:42
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I had to build something similar for two titans at 16x. Went for the threadripper which gives 64 pcie lanes. The updated threadrippers are relatively recent so probably ok to buy now. In another machine have a 3700X which is a great CPU and gives 24 pcie lanes but as per comments best to wait for 4000 series.


concordnz
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  #2503434 12-Jun-2020 10:04
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Intel are way behind with PCIe lanes - it's been a problem for 10+ years for rendering.

On Consumer CPUs
They also have a bottleneck of a 4 lane CPU 'interconnect' - which means for PCIe lanes connected via northbridge(I call it northbridge for convenience) (outside of the lanes directly connected to the cpu) - these are all bottlenecked by the aforementioned CPU interconnect - irrespective of how many lanes they may have available.
This is more & more of a problem as they try and squeeze more M.2 drives into the mix.

On Intel - you Really need to go with the Xeon or (dual CPU = Rare these days)
To get satisfactory PCIe lanes for 2 or more gfx cards & a M.2 drive.

This problem will get resolved when Intel migrate from PCIe 3.0 to PCIe 5.0 spec for their lanes give 4 x the bandwidth per lane.
This should happen in 2-3 years in the consumer space. (Servers are planned to get PCIe 5.0 in 2021)
You 'might' be able to get away with the Intel LGA1200 platform just released.
Check the design diagrams for each specific motherboard & CPU you are interested in - to confirm how many PCIe lanes are directly off the CPU & how many off the motherboard controller & bottlenecked by CPU interconnect.

arcon

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  #2503437 12-Jun-2020 10:09
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This is the most promising candidate I've seen so far at a very good price: Ryzen 7 3800X

 

From what I've read it supports 24 PCIe 4.0 lanes in CPU, with 4 reserved for the chipset connect. I know that graphics cards for gaming won't saturate more than 8X, but that's not the intended purpose so I need to put the question to my render developers about lane saturation.

 

Assuming its ok that leaves 4 lanes left... plus the 16 more delivered by the X570 chipset. Does NVME run on chipset lanes or CPU by default...?

 

 


concordnz
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  #2503443 12-Jun-2020 10:20
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As @zenourn said AMD threadripper is better - as it has more PCIe lanes directly off the CPU. (And these are actually PCIe 4.0 = twice the bandwidth of 3.0 - so they can split 8x of them to fully service a x16 gfx card slot (which are only PCIe 3.0)

Again - there are caviates with Ryzen.
CPUs are made up of 'clusters' of 4 cores - each 4 cores has 1x PCIe controller built in - if you go too cheap and get less cores - you lose PCIe lanes. (And the motherboard compensates by splitting the few available to allow all your devices to function (but not at their full potential)

So make sure the AMD CPU you chose has enough core blicks' to provide enough PCIe controllers, to provide enough PCIe lanes directly connected to the CPU.
(& of course make sure the motherboard you are looking at allows these through 'fully' & not bottlenecked.)

PCIe 4.0 has signaling distance constraints - I think 4images from CPU and it starts to degrade below spec if I recall rightly - they need to resolve this by putting in chips to re-signal/boost. - or all the channels past this chip run at PCIe 3.0 which has wider signal tolerances / longer traces.

concordnz
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  #2503448 12-Jun-2020 10:27
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arcon:

This is the most promising candidate I've seen so far at a very good price: Ryzen 7 3800X


From what I've read it supports 24 PCIe 4.0 lanes in CPU, with 4 reserved for the chipset connect. I know that graphics cards for gaming won't saturate more than 8X, but that's not the intended purpose so I need to put the question to my render developers about lane saturation.


Assuming its ok that leaves 4 lanes left... plus the 16 more delivered by the X570 chipset. Does NVME run on chipset lanes or CPU by default...?


 


Each M.2 requires 4x PCIe lanes to run at full potential.

(Most current motherboards hobble their 2nd M.2 drive to 2x lanes because there is simply not enough lanes available)
& normally the M.2 drives are run off the motherboard chip - so the M.2 is limited to 4x (total combined) by the Intel CPU interconnect anyway.

I can't recall off-hand if the Ryzen 3rd Gen motherboards run their M.2s off motherboard chip or directly from CPU PCIe controller.
(& this could vary by motherboard - you would need to check the specific motherboard design schematic you were interested in)

concordnz
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  #2503632 12-Jun-2020 13:54
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This link shows you the various options the motherboard manufacturer has on the Ryzen 3000 series.(3800x for example)

https://cdn.mos.cms.futurecdn.net/Ls8C7VapzvoeUaunNYBCEQ.jpg

CPU has 24 PCIe lanes broken down as follows
16x Graphics
4 x NMVE
4 x chipset Downlink (potential bottleneck)

& it 'may' also have the following off the CPU.
x4 NMVE (for a 2nd full speed M.2)
or
x2 NMVE & 2 x Sata (1/2 speed & more SATA)

As you can see the rest of the Options.
- (& Motherboard manufacturer must decide at time of design)
All come off the Motherboard X570 chipset
(& are all bottlenecked by the x4 PCIe downlink) - fortunately this downlink is also PCIe 4.0 so same performance as a x8 PCIe 3.0 link.

I'll try and find a similar spec layout for the Ryzen 4000 series, if I have time.

toejam316
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  #2503634 12-Jun-2020 13:57
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If you want more than 8x2 pcie lanes for your gpu, you'll need a Xeon or Threadripper system. TR3960X is 24c/48t and starts at $1800.




Anything I say is the ramblings of an ill informed, opinionated so-and-so, and not representative of any of my past, present or future employers, and is also probably best disregarded.


arcon

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  #2503669 12-Jun-2020 14:41
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toejam316: If you want more than 8x2 pcie lanes for your gpu, you'll need a Xeon or Threadripper system. TR3960X is 24c/48t and starts at $1800.

 

I haven't found a graphics card that can saturate more than 8X, so 8 lanes for each card is fine. But I think that still means consumer CPUs don't have enough lanes... 3 NVME drives = 12 more lanes, +4 reserved for chipset link = 32 total :/


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