iRacing CPU bottleneck

Apr 16, 2012
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#1
Hi all,

So I'm an iRacing fan and built myself a budget desktop for gaming and iRacing. After extensive research I finally put together a nice build, this was put together around 6 months ago. Here are the specs:

i3 2100 3.1Ghz
Gigabyte B75M-D3V
Sapphire Radeon 6850 1GB GDDR5
1x4GB RAM 1333Mhz Kingston
Western Digital Caviar Blue 500GB 7200rpm
LiteOn DVD/RW
Corsair CX500 500W 80+ power supply
Thermaltake V3 Black Edition case

Now my problem: After doing some of my own benchmarking, looking to see on which parts of the track I get the lowest FPS. I leave the car sitting in the area of lowest FPS for a while, then I minimize the simulator and check my CPU and GPU usage with Task Manager and MSI Afterburner. I do these tests at 1080p with maximum graphical settings. I also scourged the iRacing forums to make sure my settings are as optimal as possible to get the highest possible FPS.

CPU usage in Task Manager: ~90%
GPU usage in MSI Afterburner: ~80%

If I understand correctly, due to the fact that my CPU is practically killing itself... yet the GPU usage hovers around 80%... that means that my i3 2100 is the bottleneck in this case. How can I be sure that my hypothesis is correct? Are there any other components in my system that may be bottlenecking? RAM maybe?

Now what can I do to get past this issue and make sure that my system works optimally, to get rid of any bottlnecking and to make sure I get the best experience I can with iRacing? Will I have to swap out hardware? I didn't go for the i5 2500K at the time, since its price was way out of my league, and all the articles stressed on focusing on the GPU... same goes to the current i5 3570K.

I'm thinking a possible solution would be to swap out the i3 2100 and replace it with the i3 3220... from 3.1 to 3.3 Ghz + the IvyBridge architecture... should that get rid of the bottlenecking? Alternatively, I may swap out the entire motherboard and CPU, sell them, and go for an FX-4300 with an AM3+ motherboard and OC.

I would appreciate any help folks. I want my system to run optimally. I'm quite disappointed that the system I built turns out to not be as optimized as I thought it would be.

Thanks
 

boxleitnerb

Platinum Member
Nov 1, 2011
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#2
How can I be sure that my hypothesis is correct?
As you cannot overclock the 2100 (no turbo, no free multi), you would need to underclock it a little bit and see what happens with the fps:

a) Run the game, go to your spot where you determined these load values at.
b) Alt-tab out of the game, go to windows advanced energy options and lower the maximum processor state a bit:


This will affect clock speed, check with CPU-Z before and after.
c) Go back into the game and see if your fps have changed. If they have -> CPU bottleneck

The i3-3220 is still a dualcore and not much faster than the 2100. If you really need the CPU power, go with a 2500K (you need another mainboard with P67, Z77 or Z78 chipset for OC unfortunately if you go with a "K"-CPU with a free multi) or a 3570K.
AMD CPUs usually are significantly slower in gaming when you are CPU bottlenecked, I would go Intel.
 
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Apr 16, 2012
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#3
Overclock the CPU by 10% and check the fps. If they increase by ca. 10% too, the CPU is your bottleneck. A quadcore with a bit overclocking should be fine then. AMD CPUs usually are significantly slower in gaming when you are CPU bottlenecked, I would go Intel.
My motherboard is a B75 chipset... how do I overclock the i3 2100 with that? In the BIOS, I have the option of increasing or decreasing my clock speeds by 0.1 Ghz increments on the fly... however it stops increasing at 3.1 Ghz... any way to bypass this so I can overclock?

Would decreasing from 3.1 to 2.6 for example let me know if the CPU is a bottleneck?

EDIT: Ah ok I see your edited 2nd second post. Alright so I can change my clock speeds on the fly in the OS itself! Now If I find my CPU is a bottleneck... what are the options available to me?
 
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boxleitnerb

Platinum Member
Nov 1, 2011
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#4
My bad, you cannot with B75. Follow the steps I laid out, you don't need to reboot or restart the game for that. Very practical for quick checks on the fly.

The scale is not linear, so if 100% are 3.1 GHz, 50% are not 1.55 GHz, but a different value. Thus CPU-Z to be sure what frequency is active.

Edit:
Your options:

a) IF the game scales above 2 cores, a simple upgrade to a (non overclockable) quadcore might already help
b) If not, a new mainboard + CPU are in order

I'll check around if I find any more CPU benchmarks for this game. Is there a demo or something I could try out?
 
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Apr 16, 2012
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#5
My bad, you cannot with B75. Follow the steps I laid out, you don't need to reboot or restart the game for that. Very practical for quick checks on the fly.

The scale is not linear, so if 100% are 3.1 GHz, 50% are not 1.55 GHz, but a different value. Thus CPU-Z to be sure what frequency is active.
Alright, I knew before buying my parts that the i3 2100 could not be overclocked, so I chose a budget motherboard instead of one of those Z77 / Z68 boards.

I'll decrease utilization by increments of 10% and see what happens... I'm just thinking maybe... just maybe... by decreasing the utilization I'll find I don't lose performance till a certain extent... say maybe 2.6 Ghz... which would mean that something else would be a bottleneck... just thinking in advance.
 

boxleitnerb

Platinum Member
Nov 1, 2011
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#6
According to several posts on iRacing forums, the CPU seems to be more important in this game.
 

inf64

Platinum Member
Mar 11, 2011
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crazyworldofchips.blogspot.com
#7
Problem with i3s,apart from being "just" dual cores with SMT, is that hey are locked. So there is no way of increasing performance if you are CPU limited. Like others said, try downclocking and see what happens with ingame frames per second.
 
Apr 16, 2012
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#8
Hi fellas,

Alright I decreased the clock speeds my 100 mhz at a time, using the power management options and monitored with CPU-Z. Yes indeed, lower clock speeds results in lower GPU usage and in turn lower FPS.

So what's the solution now?
 

boxleitnerb

Platinum Member
Nov 1, 2011
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#9
That's a classic CPU bottleneck. Either you try to lower some options to get higher fps or you get a 2500K or 3570K on a new mainboard and overclock a little.

What fps values are you getting btw?
 
Apr 16, 2012
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#10
That's a classic CPU bottleneck. Either you try to lower some options to get higher fps or you get a 2500K or 3570K on a new mainboard and overclock a little.

What fps values are you getting btw?
Call me an idiot lol... but I'm talking about very high FPS here, in the 160 - 170 range. As time went by, I learnt that iRacing is different to games when it comes to FPS... in a nutshell, you can never get enough FPS with iRacing... since in the real world, you basically are talking about infinity FPS, which would be the ideal FPS in iRacing.

For now, my current FPS is alright for me. Now I know where my system is flawed, so when I do upgrade I know precisely what needs to be changed. At the minimum, I'll sell my i3-2100 and go for an i5 3450... should I extend my budget, I'll get a Z77 board, i5 3570K and OC that.
 

boxleitnerb

Platinum Member
Nov 1, 2011
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#11
In racing games higher FPS can be beneficial, making the controls much more direct. But 160, wow, I would not know if I could distinguish that from say 250fps :D
 

SPBHM

Diamond Member
Sep 12, 2012
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#12
2500k or 3570K and OC to 4.5GHz

I also have a 2100 and play Iracing, but I locked the framerate to 85 (I think it's the default setting)...
 
Sep 19, 2010
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www.mattkowal.net
#13
I'm not a gamer, but I always assumed that monitor refresh rates negate the benefit of extremely high fps. Can you tell the difference between 120 fps, 160fps, and 200fps? Are those peak or avg fps?
 
Apr 16, 2012
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#14
What's funny... and something I'm so baffled about I don't even know why... is that the oval races always seem to benefit from better FPS. Every time I check my usages, yes my i3 2100 is being pushed to the limit, but I get a solid 99% GPU usage in MSI Afterburner!

This situation is especially true with more cars on the grid, I always get a solid 99% GPU usage... I don't know why this is not the case with the road courses. More cars should equal more CPU horsepower is needed... but it seems my GPU is taking the load... which is a good thing for me ofcourse... but why is it happening? Any explanations?
 

SPBHM

Diamond Member
Sep 12, 2012
4,723
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#15
I'm not a gamer, but I always assumed that monitor refresh rates negate the benefit of extremely high fps. Can you tell the difference between 120 fps, 160fps, and 200fps? Are those peak or avg fps?
I suppose if the framerate is higher, you will receive a newer(as new as possible) frame on the display, so it might be a small (very small) advantage for competitive gaming,
I don't know if it's the case with Iracing, but maybe the game engine also affects physics and input based on the framerate!?




more cars should be demanding for both CPU and GPU,
I have a weaker GPU and I have some performance issues during the race starts (with many cars) if I choose to play with higher AA settings,
 

boxleitnerb

Platinum Member
Nov 1, 2011
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#16
Input is the key word here. Higher fps = shorter time between input and the result on the screen, regardless of refresh rate.
 

BrightCandle

Diamond Member
Mar 15, 2007
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#17
Just bare in mind without a change to your GPU an upgrade of the CPU is at maximum going to bring 20%, because you are already using 80% of its capabilities. There is about 2x performance available in single cards today however so its certainly possible to go quite a lot faster given no budget constraints.
 
Apr 16, 2012
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#18
Just bare in mind without a change to your GPU an upgrade of the CPU is at maximum going to bring 20%, because you are already using 80% of its capabilities. There is about 2x performance available in single cards today however so its certainly possible to go quite a lot faster given no budget constraints.
At this point I'm now thinking of the following: should I get an FX-4300 with AM3+ motherboard and OC? Or go for an i5 3570K with Z77 motherboard? I only want to get rid of that CPU bottleneck. If an overclocked FX-4300 will do the job, that's fine. I can sell the i3 2100 and B75 for a good price and put that money into buying my FX-4300 and AM3+ motherboard.

I should note my power supply is a Corsair CX500 (80+) would that be able to manage an overclocked FX-4300?
 

alexruiz

Platinum Member
Sep 21, 2001
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#19
At this point I'm now thinking of the following: should I get an FX-4300 with AM3+ motherboard and OC? Or go for an i5 3570K with Z77 motherboard? I only want to get rid of that CPU bottleneck. If an overclocked FX-4300 will do the job, that's fine. I can sell the i3 2100 and B75 for a good price and put that money into buying my FX-4300 and AM3+ motherboard.

I should note my power supply is a Corsair CX500 (80+) would that be able to manage an overclocked FX-4300?
The CX500 will power it easily.
Can the game use all the 4 cores properly? If so, the FX4300 might be faster (FX6300 suggested) If the game cannot use all the cores properly, stay intel.
 
Apr 16, 2012
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#20
The CX500 will power it easily.
Can the game use all the 4 cores properly? If so, the FX4300 might be faster (FX6300 suggested) If the game cannot use all the cores properly, stay intel.
As of now, iRacing uses 2 cores, however there are plans in the future to process sounds through a 3rd core. The main thing about iRacing is that its an absolute clock speed hog, the higher you can get the better. To test this, I reduced the clock speed of my 3.1Ghz i3 2100 by 100Mhz increments at a time. Each decrease gave the sim quite a whack and brought FPS down by about 10 at a time.

I understand the FX-6300 is a viable choice, 2 extra cores for only $10 more. But I want to to be absolutely sure that an overclocked FX4300 / FX6300 will get rid of the bottlenecking and possibly allow me to overclock my 6850... otherwise there's no point in swapping out hardware.
 

boxleitnerb

Platinum Member
Nov 1, 2011
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#21
CPU performance is determined by clock speed and IPC (performance per MHz). AMD CPUs have significantly lower IPC than Intel CPUs while not really clocking that much higher. I would guess any FX CPU would have to be clocked at around 4-4.5 GHz to tie your 3.1 GHz i3. So it wouldn't really make much sense to take the FX. You might get 5 GHz out of it, but that would only be 10-15% faster than what you have now.
 
Apr 16, 2012
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#22
Ok fellas, now I am completely baffled!

Only yesterday, I was complaining about my i3-2100 not being up to par pushing the 6850 to the limit, with the GPU reaching a mere 70% - 80%, and the CPU fighting at around 90%.

Today I fired up the sim as usual. I was completely baffled to find my FPS running a good bit higher than usual at the same graphical settings, and even more so when I found my GPU usage pegged at a consistent 99%, with the i3-2100 sailing along at about 50%.

So... what in the world happened?! Where did I get this mysterious boost in power?! I can now run comfortably with a group of 20 cars and never see my FPS dip below 120! And this is at 1080p!
 

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