Will increasing base clock (BCLK) give better crossfire/sli performance?

Enhanced Interrogator

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Say I have a mother board where the PCIE 3.0 drops to 8x with crossfire, could I feasibly be bottlenecked there and thus help myself with a faster BCLK?

Because right now I have my CPU and RAM on higher multipliers while leaving my base clock untouched.
 

DrLobotomy

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I doubt it. BCLK is not the friend you think it is. Most modern boards now get unstable when you try to mess with the BCLK. Pretty sure the diff between 8x and 16x is minimal. But since we have no idea what chip, board brand & model then no clue.
 

Nenu

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You are talking a few % max in a very limited scenario, of which there are practically none.
And as pointed out, you may risk stability.

PCI-e 3.0 x8 is the same bandwidth as PCI-e 2.0 x16, neither bottleneck single cards.
PCI-e 3.0 x8 has a slight advantage because the clockrate is higher, its response is slightly faster / latency is lower overall.
So you have most of the benefit already.
 

Enhanced Interrogator

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Yeah, the one time I tried to increase BCLK by 20% I couldn't POST, but that may be because I didn't change voltages enough. I have Gigabyte z170xp-sli, which is a lower end multi-gpu board. Running with Xfire 380x's, 2x8gb RAM at 3000mhz CL15 RAM, and a 6600k currently OC'd at 4.3ghz

I just remember reading a few years a go that a 1:1 RAM to FSB ratio was preferrable. Like, you reduce RAM frequency but increase timings (and BCLK) to get a 1:1 ratio with a similar overall memory speed. I guess that's not a big deal anymore? Or is it just too difficult for modern boards?
 

Nenu

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Its less of an issue because frequencies are so high, there is hardly any increase in latency waiting for a clock cycle to occur.
Not worth the effort.
 

Enhanced Interrogator

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Thanks for the advice. My main issue is that I'm still hitting some sort of CPU/system bottleneck in hectic firefights in BF4. Not sure if my GPU's are maxing out, forcing my CPU to wait, or if it's something else.

I'm running all Ultra at 85hz so I expect to hit a wall from time to time, but I always like tweaking to see if I can move the wall further back.
 

Nenu

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Use MSI Afterburner to graph CPU per core, memory and GPU use.
It can also show PCI-e bus, pagefile use, GPU power limit etc.
Then you can see what is hitting the wall.
 

Enhanced Interrogator

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BF4's built in tools are pretty great, showing graphs of GPU and CPU frametimes. The extra stuff in Afterburner might be useful though.
 

Dan_D

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Z170 has the PCIe bus unlinked from the base clock frequency. X99 and older chipsets do link them, but more than 1-3MHz will cause you instability in most cases. Knock yourself out, but it won't get you anything.
 

cyclone3d

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Yeah, the one time I tried to increase BCLK by 20% I couldn't POST, but that may be because I didn't change voltages enough. I have Gigabyte z170xp-sli, which is a lower end multi-gpu board. Running with Xfire 380x's, 2x8gb RAM at 3000mhz CL15 RAM, and a 6600k currently OC'd at 4.3ghz

I just remember reading a few years a go that a 1:1 RAM to FSB ratio was preferrable. Like, you reduce RAM frequency but increase timings (and BCLK) to get a 1:1 ratio with a similar overall memory speed. I guess that's not a big deal anymore? Or is it just too difficult for modern boards?

What is the load on the GPUs and CPU when you are having slowdowns?

How much video RAM is being used when you have the slowdowns? Could be you are running out of RAM on the video cards.

Also, your dual channel RAM setup could be the bottleneck.

Not sure if it has changed, but the older BF games really loved RAM throughput. On a triple channel setup, going from 1066 to 1333 to 1600 made quite the difference. Your dual channel setup at 3000 has less throughput than an x79 quad channel setup running DDR3-1600 (you would need DDR4-4000 to match a quad channel DDR3-1600 setup).

I would set up MSI Afterburner to monitor system loads. If you have a second screen, open it up on that. If not, then alt-tab out when you have a slowdown and take a look.

Are you running full screen or windowed?
 

Enhanced Interrogator

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Running fullscreen, crossfire with Mantle API (which is supposed to reduce CPU bottlenecks). My VRAM usage was topping out around 3.3GB and I have 4GB, so I should be good there.

I haven't looked at the frametime graphs enough, but usually my CPU begins drop frames when my GPU's frametimes get really high (i.e. slower than my refresh rate). I have Vsync on, so that is typical. But I think I may have noticed a few scenarios where the GPU's were keeping up but the CPU would drop a few frames.

So this is a <1% of the time issue (like when a tank is blowing up 5 feet from me), so I'm fine with it where it is, but I'm always interested in seeing if I can smooth out performance even more. I'll try loading up MSI on a second monitor sometime and see what's really going on.
 
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