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GPU latency test

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#1
Is there a way to test the latency of a GPU? I'm looking to add a PICe extender cable. Also would be neat to know the difference between the closest PCIe slot and the farthest.
 
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#2
I guess the only way to test it is accually noticing it in regular use
 

Bo$$

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#3
Is there a way to test the latency of a GPU? I'm looking to add a PICe extender cable. Also would be neat to know the difference between the closest PCIe slot and the farthest.
No generally not latency, you'll see a speed decrease depending on your motherboard. I don't think you can check PCI-e latency, although there is a DPC latency which might be what you are looking for
:toast:

http://www.thesycon.com/deu/latency_check.shtml
 
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#4
I don't know if this helps, but the game called Path of Exile has an option to track you GPU latency and GPU fps. Mine is 16-17ms in this game (yeah, i'm actually talking about GPU latency, not network). Currently the game is in closed beta so u would have to pay in order to play but in around a month it will be f2p.
 

W1zzard

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#5
that's frametime.. the time to render a whole frame, not the bus latency

as far as i know there is no software to measure it. your enemy is not latency but signal integrity. i would say adding up to 10 cm should be no problem at all, beyond that, give it a try and see if the card is stable
 
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#6
I think with most MBs and cases it's more a question of whether the secondary slot you use supports 8x or 16x and whether using the farther one for spacing/cooling purposes allows expansion slot venting and PSU clearance, not to mention MB component clearance of those bottom ports you need to plug into for front panel, USB, etc. Regarding 8x vs 16x, it doesn't matter as much on modern Pci-Ex 3 MBs though because 8x on those is the same bandwidth as 16x on the Pci-Ex 2 ones.

A lot of people don't want to use the 2nd Pci-Ex slot, which typically has the 2nd GPU crammed right next to the first one, and with some so called dual slot GPUs, like Sapphire's 7000 series, the card shroud hangs out too far to even use the 2nd slot. My P6X58D-E MB is designed with a close 2nd slot and one near the bottom of the MB. I have clearance above my PSU and can even clear the small cables connected to the bottom of the MB if I don't use the Q-Connector, but my case has no exhaust slot on the expansion ports that low, and I'd have to buy a super long (like 120mm) bridge connector to connect the GPUs. The next MB I get will probably have a 2nd lost that is not right next to the first. I have to say using two video cards is more of a last upgrade resort for me though, and I've yet to bother with it.

TPU has done some Pci-Ex bandwidth tests comparing FPS between 8x and 16x slots on the old Pci-Ex 2 MBs when GPUs started exceeding 8x bandwidth, but as far as I know no such tests have been done since the 580 and 5870. If I recall correctly the 580 lost about 2% of it's FPS on 8x vs 16x. Again though, that is on Pci-Ex 2. On Pci-Ex 3 8x isn't an issue at all.
 

eidairaman1

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#7
PEG 8X and 16X whether 1.0 spec or higher are Ideal for Video, PEG 4X is a major bottleneck. Just means Always Use PEG 8 or 16 but never 4.
 
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#8
that's frametime.. the time to render a whole frame, not the bus latency

as far as i know there is no software to measure it. your enemy is not latency but signal integrity. i would say adding up to 10 cm should be no problem at all, beyond that, give it a try and see if the card is stable
Speaking of signal integrity, would the 75w power draw off the PICe slot pose an issue with the ribbon? I mean in theory; "made in China" may have other plans.

I got thinking about a way to solve the latency issue: A 10 cm ribbon should add 0.67ns round trip plus any loss at the junctions. Speed of light: 299,792,458 m/s * 5 = 1,498,962,290 (number of 20 cm round trips). 1 s = 1,000,000,000 ns. 1 / 1.498962290 =~ 0.67.
 

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#9
would the 75w power draw off the PICe slot pose an issue with the ribbon?
there would be some heat dissipated in the power lines in the extender due to the extra length, it shouldn't pose any problems though