PCI Latency Timer can increase fps.

filmoret

So I was messing in bios and noticed I have something called a PCI Latency Timer and after a few google searches they seem to do with interrupts with the pci slots.  I was wondering if anyone knows when you only have 1 pci slot should you set this to max or would it even matter?  From what I have read if this number is set wrong it can hamper fps in a lot of video cards.

Quizzical

If you have to ask, then you should leave it at the default.

holdenhamlet

I've tried tons of fps fixes due to trying to work with budget video cards and I've never heard of this.  Probably best not to mess with it.

filmoret

Ok my system is set at 32 which is lowest.  So I ran benchmarks at lowest then set it at highest and inbetween a few places.  Didn't make the benchmarks any better for me.  Now I will try a game and see if there is any difference.  It has something to do with interrupts between pci slots I believe.  It gives each slot longer to compute before switching to another is the rumor. 

Ridelynn

Seems like we've seen this before, but for the life of me I can't find the thread, it was a year or two ago.

Anyway, long story short - there used to be a fellow that would come here. He was a nice guy, but a bit... eccentric: @drbaltazar. I'm sure a lot of people who have been here a while know exactly who I am talking about.

He would commonly come up with something like this - my game is {lagging/studdering/looks blue/pick a problem} so it must be {PCI latency timer/CPU C-States/NIC overclock/aliens/pick some random and obscure thing}

So he would post about it. We would all say something more common sense, but he was undaunted, and would go down his path, for better of worse. After a few posts, he would have fixed the problem, and of course, his constant game lagging was caused by changing his PCI Latency setting and disabling the invariant TSC (or whatever it was he initially suspected all along). 

And then, a few days later, he'd have some other problem. Probably caused by his tinkering from the first. And it just kept compounding over the months.

Morale(s) of the story - Defaults are set to default for a reason, because they usually work. The correct explanation is usually the simplest. 

Now I'm all for tinkering with your own hardware and seeing what does what. Go for it. And let us know what you find out. Just do enough research before hand that you don't get yourself into a predicament where you can't unwind back out of it and end up damaging something..

filmoret

I found this and its definitely something to think about.  I mean there is no need to ignore something that could possibly be hindering your pci slots.  And nowhere have I seen that it can cause any kind of damage.

Quote:

PCI latency timers are a method to allow PCI bus-mastering devices to share the PCI bus so that PCI devices won't use such a large portion of the available PCI bus bandwidth that other devices aren't able to get needed work done. 

If you have problems with your audio (usually onboard) clicking (while overclocking especially) then setting PCI latency timings to a more mid-range can help set the PCI bus fairly and allow for concurrent requests to be handled in que, giving the audio a better chance to respond to the signal reqeust and hence data delivery. 

Hence the audio and other PCI bus issues that can be problematic, and especially so in an overclocked system which can often be attributed to the PCI latency settings.

If the Latency Timer is set too low, then PCI devices will interrupt their transfers unnecessarily often which will effect performance. If it's set too high, devices that require frequent bus access may overflow their buffers and lose data. This is where you will hear crackles in sound and dropped packets in Lan data transfers or web access. 

If you are having issues you can set the access (I use 48 clock cycles) and test for issues.


http://www.tomshardware.com/forum/261724-29-latency

Quizzical

Ridelynn said:

Seems like we've seen this before, but for the life of me I can't find the thread, it was a year or two ago.

Anyway, long story short - there used to be a fellow that would come here. He was a nice guy, but a bit... eccentric: @drbaltazar. I'm sure a lot of people who have been here a while know exactly who I am talking about.

He would commonly come up with something like this - my game is {lagging/studdering/looks blue/pick a problem} so it must be {PCI latency timer/CPU C-States/NIC overclock/aliens/pick some random and obscure thing}

So he would post about it. We would all say something more common sense, but he was undaunted, and would go down his path, for better of worse. After a few posts, he would have fixed the problem, and of course, his constant game lagging was caused by changing his PCI Latency setting and disabling the invariant TSC (or whatever it was he initially suspected all along). 

And then, a few days later, he'd have some other problem. Probably caused by his tinkering from the first. And it just kept compounding over the months.

Morale(s) of the story - Defaults are set to default for a reason, because they usually work. The correct explanation is usually the simplest. 

Now I'm all for tinkering with your own hardware and seeing what does what. Go for it. And let us know what you find out. Just do enough research before hand that you don't get yourself into a predicament where you can't unwind back out of it and end up damaging something..

This thread reminded me of him, too.  He went on for quite some time about msi-x.  For example:

http://forums.mmorpg.com/discussion/396212/xbox-1-question