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Chaning PCI/AGP latency

G

germanjulian

n00b
Joined
Jul 22, 2004
Messages
58
Hi, my first post so I thought I do something special. I found out something yesterday and was playing around so here:

UPDATE:
OK, the latency for the AGP bus for ATI cards is indeed 255! even when you select 32 in your BIOS.
if you search your registry for DisableProgPCILatency and change the value from 0 to 1 this will be changed on the next restart to 32!!!!
You can check your latency of all buses with this program:
http://www.transformerman1.plus.com/LtcyCfg.zip

What the author or the article below claims is that this fixes some stuttering in games but moreover get rids of audio popping and cracking issues, due to some devices taking up to much CPU time (high latency).
with the program you can also change the latency from 32 to another you desire (remeber it has to something which can be devided by 8).

Anyway I tested it only with Colin McRae 4 which I found stuttered very much for me (very little stutters) even though I had 50FPS. WIth this tweak the stutters are gone!

Never experienced stutters with other games before but hey it does not hurt graphics performance! (tested with 3dmark03).

anyway try it if you want:





http://www.transformerman1.plus.com/LtcyCfg.zip

Get the tool and see if your graphiccard is running at 248ms latency. Is it?

Decrease latency of it (or any other device with a latency, '000' means: has none) to 64 or below (below may not be faster, depends on system) and go into your favorite 3D game!

Any difference? I say YES and put my hands in fire for that.

Note that you can save the config it to a file (click 'add to list first' or it won't work) and load it via batch file (read me) when windows starts because otherwise windows will overwrite your settings with the next boot (JUST LIKE IT DOES WITH YOUR BIOS SETTINGS! GRMMF!)

Ok, to clear some things up.

1. The changes apply for AGP also!
2. You do not have to do it after every boot.

a) Start program and make the changes you want (enter number and click 'set now' for the device you want to change) - make sure you don't touch the devices that don't have 000 (no) latency at all
B) mark ALL entries and click on 'add to list', you will see a new column called 'new' on the right (means it's added)
C) press 'save as' and save the table to a config file with a name you like into the program folder I suggest
d) Go into the program folder, create a txt file and write into it:

C:\LtcyCfg\LtcyCfg.exe -f:C:\LtcyCfg\config.cfg <- Replace with your path and name of config file of course. (I think you could leave the folders away as the file resides in the same directory of the program, but I never trust windows in such cases)

Then save the txt-file and replace it's extension with BAT (if you can't see the extension you'll have to go to your windows-explorer->extras->folder options->somewhere...Google if you don't know and disable the 'hide extensions from known file types' or whatever it's called in the English version of XP)

e) Drag a shortcut of that BAT-file into your auto start folder

f) Done, if you want to make changes repeat step a-c. Happy gaming and more overall power (even on desktop)

3. Possible heat problem: I WOULD say no. Me and my friends (one doesn't even have a fan on his ATI!!!) didn't encounter any problems but only improvement of performance.

Let me try to explain why (simple words, I'm no technician):

Decreasing the latency does NOT mean INCREASING the response time of your hardware!

The BUS latency stands for: How much time does a component of your PC (graphic card, network card, and sound card) have to perform an operation before another component can! Note that only one component can use the BUS at one time, then the next, then the next. In other words: instead of letting your graphic card do 100 operations in 248ms you set it to a lower number of operations in 32, 64, 128ms. (32 is minimum and must be a number that



can be divided by 8)

So the problem is while leaving the graphic card latency at 248ms - which it is mostly set to - that the component has TOO MUCH time and other important operations (soundcard for example) can not be performed in time, so the queue list is getting bigger and bigger-> CPU overload.

Experiment a little with the settings and see what gets you best performance. In my opinion it's mostly the graphic card latency that hogs the CPU but you may tweak a little more out of it. Depends on hardware I guess. I have all my components set to 32ms now.

For more info go here: http://www.mark-knutson.com/technique_to_target_inc/ (Note that at this URL you'll find another program called PCIDAWG. It does exactly the same but has no possibility of loading it with windows, anyway the information you'll find there is pretty good. It's written by the programmer of PCIDAWG)

- - - - -
ADDED SOME MORE INFO:

Some of you might wonder why you have the "PCI Latency time" option in your BIOS if the PCI latency is messed up if you don't use a program like this one here.

1. Windows overwrites this setting. *Duh*
2. Some manufacturers of graphic cards and (possibly other hardware) set the latency of their cards to 248ms internally on the card itself (the programmer of PCIDAWG says that they do it to boost performance and that they are obviously wrong with that in most cases)

Who knows why they didn't play out THAT joker by now. ; )
- - - - -

One more thing: Don't blame me for a blown up card. I do not expect this to happen as I made only (and many) good experiences by tweaking these settings on many different PC systems. I tried to explain why hardware damage is probably never going to happen above BUT AT LAST: I'm no technician and no graphic card manufacturer.
 
... somebody correct me if i'm wrong, because maybe i'm missing something, but wouldn't this tweak only have an effect if the devices on the bus in question (vid & sound) are sharing the same IRQ?
 
Just tried out this tweak, using powerstrip to change the latency on my vid card from 248 to 64, and now I have noticably smoother gameplay in Farcry. The card I am using is a GF4Ti4200, overclocked to 300/570.
 
Just verified via fraps that I'm getting the exact same average framerate in Farcry as before (33 fps @1024, every game setting except texture quality set to "very high", anti aliasing & ansitropic filtering off) ...framerate is the same, but the game feels about 20fps smoother... if that makes any sense.

After some device manager investigating, I noticed that my USB controller that my mouse is plugged into is using the same IRQ as my videocard, but from what I can tell, this tweak shouldn't have done anything for me, considering the USB controller already had a latency of 0, and my AGP card resides on bus 1, and the USB is bus 0. Could my vid card latency really have been that much of a hog as to impact mouse performance? Someone tell me I'm not just imagining this smoothness increase.

I guess the bottom line is that this tweak has noticiable effects. Either that or it combines with my sleep deprivation to form an awesome placebo effect.
 
well I second your finding. colin is much smoother.

oh and dont use powerstrip to change it. just do the registry tweak! cause powerstrip uses loads of CPU power when doing this apperantly!!!!

funny that I never knew device drivers can overwritte the pci latency set in the bios. now all is set at 64!!! and smooth.
 
well I did some more testing.

I get the same FPS (and I mean exactly)

I run Mother Nature test,
Pixel Shader 2 test
and all 3 Sound tests

I get the same FPS with 32, 64, 254 latency. Though in the last two sound tests I got 0.1 FPS more with 64 and 32 latency then with 254 latency but I suppose thats a margin error with 3dmark03.

I also played some more games and Colin does stutter sometimes still but I do think its a little better. FarCry is still smooth and so is UT2k04.

So maybe it is plocebo maybe not!? But on the forums I have been researching some people do say this fixed sound issues and stutter problems for some.
Anyway it does not degrade performance whatsoever and I like it that my sound card now gets the same time for using the CPU then my grahics card. :D bit unfair 254 for graphics card and 32 for eveything else.... pprrrhhhhhh
 
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