CPU bottleneck, highend GPU a myth?

[zuludawn]

Here goes after many weeks of observations

I have had a random bluescreen off death for two months now, have narrowed it down to motherboard (Gigabyte X58 Extreme) or the CPU (i7 920 @ 4gig)

All examples were done using 2 x XFX 7970 Black, stock and overclocked.

Highest Unigine score was 148 fps 1060X1050 and lowest was 142fps all overclocked, all backed up by BF3 (most popular game at the moment) multi using Fraps. BFS was at 2560x1440 all results around 60fps everything maxed out to the limit.

Observations

1. going from 16X16 lanes to 8X8 lost about 3fps (but 10 degrees cooler on GPU 1))

2. going from stock GPU`s to 1125-1575 gained 12fps

3. going from stock to maxed out mem settings 7,7,7,24 to 8,8,8,24, to 9,9,9,24 up to 9,11,9,27 made about 4fps

4. going from 191x20 plus turbo BCLK to 20 x20 made no differance.

5. going from 200x20 BCLK to 191x200 only dropped 3 fps

So to the latter, where is CPU bottlenecking with this setup it only drops 6fps from 4.1 gig at my highest to 3.8 gig in Unigine and BF3 2560 X1440. So with highend GPU does it really matter the speed of the CPU after all. So on that note going from i7 4 gig CPU to 2500k at 4.6 gig may only get you around 10fps extra, which you can gain from a simple GPU overclock anyway

Other games played, tested

Aliens ver Predator
Crysis and Crysis 2
Skyrim
Far Cry 2

Final word, with weeks of tweaking everything i only ever made 6fps difference from my lowest score a i7 3.8 gig mem at 1240mhz to the highest score at 4.1 gig mem at 1800mhz, GPU a speeds all the same. So the morale of the story may be to just bang in Highend GPU into you're existing system, you may not need to upgrade everything else.

i7 x58 still has plenty of life left in it. ( if you mad enough to shove £900 of GPU into (IF YOU WANT MAXED EVERYTHING AT 2560X1440), but still cheaper than a new system upgade `:¬)

You may get the gist of it or not lol (no matter what i did CPU, Bios tweaking games still got 60fps 2560x1440 with pure GPU power)

 

[zuludawn]

Thanks for the observations Zulu.

I thought the i7 didn't like even multipliers hence your BSODs?

I have mine at 21 x 191. And never experienced any BSODs with my 920 DO.

Has been 100% stable for about 2 years or so , since i first had it, is either the cpu given up, or problems with the motherboard, thats why im playing about with it so much.

 

[zuludawn]

Unfortunately you haven't said an awful lot of anything.

Why 60fps, are you running with vsync enabled in BF3, in which case you could be dropping from 120 to 80fps but both being limited to 60fps, you're not seeing a difference. Also 3fps, 6 fps, aren't great markers of how much performance that is. 6fps is a tiny difference at 150fps, and a pretty massive difference at 30fps.

uniengine is pure gpu power, it will kill pretty much any setup and show very little cpu difference, games aren't built the same way, very few will stress the gpu's or be so completely gpu dependant.

Your cpu isn't 3.8Ghz at stock, (from what I remember anyway), why not test 3Ghz vs 4Ghz, no vsync, in 2-3 games and see what difference in performance you get.


In general most games aren't cpu limited either at all, or badly, that has been the case for donkeys years, simply because you buy a gpu for a resolution/setting.

If you've got a single 7970 gettign 60fps in Bf3 at 1920x1080 maxed out, and you're not cpu limited, you could likely drop to 1280x1024 and see that you're "stuck" at 100fps, and purely cpu limited. The simple thing being you wouldn't run at that resolution. LIkewise if you buy a second 7970, you generally don't do it to get 120fps at 1920x1080, you generally do it to bump up the resolution, use a bigger screen and/or increase settings depending on the game.

one 7970 might not be CPu limited in 99/100 games at 1920x1080, 2x7970's might only be not cpu limited in 60/100 games at the same res, but the vast majority of people using 2x7970's will be running a bigger screen, or whack the AA/settings up to a point where you are again only cpu limited in 99/100 games.

I don't think there has been a time in the past 15 years where spending more than £150 on a cpu has made any real difference to gaming performance. Years ago that is a decent single core, later, a decent dual core, and now a low end quad core is fine.


Basically, 3Ghz vs 4Ghz, pick a game with fantastic xfire scaling(not sure if that is the case with BF3 or not these days), keep the same memory timings/speed and run max/stock gpu settings at each clock speed. I have a feeling BF3 isn't the best game to show up a difference, others will likely show a better difference. Skyrim might show a big difference between 3/4ghz.

You said a lot of nothing, basic idea is to spend cash on GPU and not CPU simples. If you read it, examples would be made against i7 4 gig and 2500k at 4.6 gig which would be more beneficial than 3 gig to 4 gig with highend GPU`S, get my drift!!!!

Did you also miss the other 5 games i also mentioned as well????

Plus all the Bios tweaking in the world may only gain 3 or more fps, just aint worth it.