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Is the PCI latency timer relevant if I only have one PCI device?

Tags:
  • Latency
  • PCI
  • Devices
  • Motherboards
  • BIOS
Last response: in Motherboards
June 9, 2013 8:06:06 PM

Title pretty much says it all: Is the PCI latency timer setting in the BIOS relevant if I only have one PCI device? I've got one PCIe3 video card (Radeon HD 7950) hooked up; no discrete audio or anything else like that. Super simple.

I've noticed a substantial amount of lag in places when playing bioshock infinite, which really just shouldn't be the case. This couldn't be the culprit, though, could it?

My presumption is that if there's only one PCI device, then it shouldn't make a difference, but I don't know if perhaps every 32 clock cycles, for example (if that's the setting of the latency timer), some kind of check is performed to see if any of the other slots have any data to send, and I'm losing PCI bandwidth on empty checks... I'd love for someone to share their expertise with me :) 

My motherboard is an MSI Z77A-G45:
http://www.msi.com/product/mb/Z77A-G45.html
2 x PCIe 3.0 x16 slots
1 x PCIe 2.0 x16 slot (only supports up to x4 speed)
4 x PCIe 2.0 x1 slots

More about : pci latency timer relevant pci device

August 6, 2013 3:40:05 AM

SyntaxSocialist said:
Title pretty much says it all: Is the PCI latency timer setting in the BIOS relevant if I only have one PCI device? I've got one PCIe3 video card (Radeon HD 7950) hooked up; no discrete audio or anything else like that. Super simple.

I've noticed a substantial amount of lag in places when playing bioshock infinite, which really just shouldn't be the case. This couldn't be the culprit, though, could it?

My presumption is that if there's only one PCI device, then it shouldn't make a difference, but I don't know if perhaps every 32 clock cycles, for example (if that's the setting of the latency timer), some kind of check is performed to see if any of the other slots have any data to send, and I'm losing PCI bandwidth on empty checks... I'd love for someone to share their expertise with me :) 

My motherboard is an MSI Z77A-G45:
http://www.msi.com/product/mb/Z77A-G45.html
2 x PCIe 3.0 x16 slots
1 x PCIe 2.0 x16 slot (only supports up to x4 speed)
4 x PCIe 2.0 x1 slots


Hello, that is quite a coincidence I was surfing around the internet for an explanation to the PCI latency timer issue since I recently purchased the same motherboard :) , it was for an upgrade and found the MSI Z77A-G45 its quite great and while I was checking the bios I stumbled upon this option, how do I want to set my PCI latency? then the more obvious thing to ask was how good will do to me?! since I am in your shoes, I only have one PCIE plugged my video card, an MSI GTX56ti HAWK EDITION.

So will you guys please help, I read many articles about the issue but I am still boggled buy if it is to be adjusted in our case or just leave at default setting. Thanks.
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August 7, 2013 6:50:20 AM

dfox79 said:
Hello, that is quite a coincidence I was surfing around the internet for an explanation to the PCI latency timer issue since I recently purchased the same motherboard :) , it was for an upgrade and found the MSI Z77A-G45 its quite great and while I was checking the bios I stumbled upon this option, how do I want to set my PCI latency? then the more obvious thing to ask was how good will do to me?! since I am in your shoes, I only have one PCIE plugged my video card, an MSI GTX56ti HAWK EDITION.

So will you guys please help, I read many articles about the issue but I am still boggled buy if it is to be adjusted in our case or just leave at default setting. Thanks.


Best advice I've found on the matter is here. Basically, just leave it be. If there are issues in-game, try changing the latency setting; it won't do any harm. If that solves the issues, then bingo! If not, then clearly the issue is rooted in something else and you can leave it at the default setting.

Hope that helps :) 
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November 17, 2014 7:24:50 PM

SyntaxSocialist said:
Title pretty much says it all: Is the PCI latency timer setting in the BIOS relevant if I only have one PCI device? I've got one PCIe3 video card (Radeon HD 7950) hooked up; no discrete audio or anything else like that. Super simple.

I've noticed a substantial amount of lag in places when playing bioshock infinite, which really just shouldn't be the case. This couldn't be the culprit, though, could it?

My presumption is that if there's only one PCI device, then it shouldn't make a difference, but I don't know if perhaps every 32 clock cycles, for example (if that's the setting of the latency timer), some kind of check is performed to see if any of the other slots have any data to send, and I'm losing PCI bandwidth on empty checks... I'd love for someone to share their expertise with me :) 

My motherboard is an MSI Z77A-G45:
http://www.msi.com/product/mb/Z77A-G45.html
2 x PCIe 3.0 x16 slots
1 x PCIe 2.0 x16 slot (only supports up to x4 speed)
4 x PCIe 2.0 x1 slots


Quote from the manual (I own this board too!!)
"PCI Latency Timer
Controls how long each PCI device can hold the bus before another takes over. When set to higher values, every PCI device can conduct transactions for a longer time and thus improve the effective PCI bandwidth."

I can not do anything more than speculate at this point. Thought I would share to see if it gives you a clue or two ;)  According to this, you get better bandwidth with a higher value for your one PCI device. I'm sure you've tried already and noticed whether or not your experience was affected.
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