[Question] Types of bottlenecking & their remedies?

[Kratos47]

So can anyone provide some good info on this subject? I have heard this term plenty of times and i do know a little bit but nothing in concrete terms.

How does components like GPU or CPU become bottlenecks? Under which scenarios? How can one resolve these issues to get more fps if and when we encounter this.

Does screen resolution also play a significant factor in this?

I would appreciate if someone can link me a good source material which provides some layman insight about this.

 

[Morbus]

Bottlenecking happens whenever one of the components of your system isn't performing to the full of its capabilities. It is an inevitable thing to happen. Let's put it simply:

When a game is running:
- CPU at 40%
- GPU at 100%
- HDD at 2%

In this case, the bottleneck is in the graphics card. That means you won't see (meaningful) performance improvements if you get a better CPU or HDD. Here's another example:

When a game is LOADING:
- CPU at 70%
- GPU at 10%
- HDD at 20%
- RAM transfer at 100%
- RAM usage at 50%

This means the RAM bandwidth is the bottleneck, and you need faster RAM. If you upgrade your CPU, you'll still probably see some improvements, but they won't be that meaningful when compared to RAM. Another possible situation is this:

When a game is LOADING:
- CPU at 70%
- GPU at 10%
- HDD at 100%
- RAM transfer at 100%
- RAM usage at 100%

This means both the RAM and the HDD are the bottleneck, but the HDD usage is so high probably because you're paging, i.e. your RAM is maxed out and you're using your HDD instead. In this case, installing more (not necessarily faster) RAM will give you an improvement to performance.

All in all, depending on what you're doing, you'll always have a bottleneck somewhere. It's impossible that everything is running at 100%. I myself prefer to be GPU limited, while spending as much as I can (feel I need) in the GPU front. If you have a nice graphics card and you're still GPU limited, that means the rest of your system will probably handled at least one GPU upgrade in the future without requiring you to upgrade something else.

Also note that sometimes nothing is running at 100%. This may happen because either what you're running isn't that hard to run (like a movie or something), but in games it usually means your frames per second are capped by your monitor's refresh rate. In this case, your monitor is effectively the bottleneck

 

[Kratos47]

Thanks for the explanation.

So if lets say, while gaming, my CPU is at 100% while GPU is 45%, then does it means that my CPU is being bottlenecked? And under these circumstance would overclocking CPU improve fps?

 

[Mand]

Thanks for the explanation.

So if lets say, while gaming, my CPU is at 100% while GPU is 45%, then does it means that my CPU is being bottlenecked? And under these circumstance would overclocking CPU improve fps?

The thing that's being bottlenecked is the thing that is not running at 100%. The thing that is running at 100% is the bottleneck, the thing that is below 100% has room to grow if you make improvements elsewhere.

 

[Kratos47]

Ah lets say, i'm running Total War Rome 2 game, which is said to be CPU intensive. I'm using my CPU@2.66GHz on 100% load while the GPU rests at 46%.

So under this scenario, my GPU is being bottlenecked by my CPU, which is the bottleneck? Did i get this right?

And if i say OC my CPU@4.2GHz, then would i give more breathing space to my GPU, to get more fps?

 

[Termie]

snip

Excellent explanation above by Morbus.

Thanks for the explanation.

So if lets say, while gaming, my CPU is at 100% while GPU is 45%, then does it means that my CPU is being bottlenecked? And under these circumstance would overclocking CPU improve fps?

The one situation he didn't mention is yours, where the CPU is the bottleneck. But if a CPU is at 100% and a GPU is at 45%, the system is very much out of balance. Assuming the average CPU can only overclocked 15-20%, this system would never be running optimally in games (i.e., have GPU at 100%, which is what you want). But yes, overclocking the CPU will certainly help, you just won't get your full money's worth from the video card.

 

[BrightCandle]

There is another problem though - which is that games don't typically use multiple cores of a CPU very well. So you can have the GPU reading 50% and the CPU reading 25% and still be CPU bottlenecked. That is because the overall CPU usage you see is for all of the cores on your CPU, and yet the game can only use 1 or 2 of them and is struggling to keep the GPU busy. The CPU is the limit of the games FPS, turning down purely graphical features wont help improve performance at all.

Its also worth mentioning that a lot of graphics options are also CPU related. The program running on the CPU has to setup the GPU, and some of the graphical features rely heavily on the CPU performance. So sometimes it can be the case that changing one graphical setting increases FPS despite the CPU limitation, because it turned out the graphical effect had a heavy use of the CPU element to it.

There is no simple tool to show you the bottlenecks unfortunately, all we really have is GPU usage, CPU usage and overclocking to determine the extent of finding what is the limiting factor and which part to upgrade would be most beneficial, which differs game to game.

 

[Termie]

Ah lets say, i'm running Total War Rome 2 game, which is said to be CPU intensive. I'm using my CPU@2.66GHz on 100% load while the GPU rests at 46%.

So under this scenario, my GPU is being bottlenecked by my CPU, which is the bottleneck? Did i get this right?

And if i say OC my CPU@4.2GHz, then would i give more breathing space to my GPU, to get more fps?

Absolutely correct, though overclocking a 2.66GHz CPU to 4.2GHz is unlikely. A few i7-920 chips were capable of that, but for the most part, that's going to an unrealistic goal.

 

[Morbus]

Thanks for the explanation.

So if lets say, while gaming, my CPU is at 100% while GPU is 45%, then does it means that my CPU is being bottlenecked? And under these circumstance would overclocking CPU improve fps?

Indeed, the CPU would be THE bottleneck, and overclocking would improve FPS.

Terminology-wise, the CPU would be the bottleneck, and everything else would be bottlenecked.

Ah lets say, i'm running Total War Rome 2 game, which is said to be CPU intensive. I'm using my CPU@2.66GHz on 100% load while the GPU rests at 46%.

So under this scenario, my GPU is being bottlenecked by my CPU, which is the bottleneck? Did i get this right?

And if i say OC my CPU@4.2GHz, then would i give more breathing space to my GPU, to get more fps?

Yes to all, but the difference when overclocking the CPU won't be so great that you're suddenly changing where the bottleneck is. Tipically, only upgrading your CPU will ensure that the GPU is the bottleneck. Overclocking should still give a FPS boost though.

Excellent explanation above by Morbus.

Thank you!

anyway, the whole issue is quite hard to explain and grasp. Even inside the graphics card, when it's the bottleneck, you could be VRAM limited, shader limited, raw GPU power limited, you could be bandwidth limited... Or the CPU, may be thread limited, or raw single-core power limited...

 

[Concillian]

Keep in mind that something is ALWAYS a bottleneck. If a game is running at 2000 FPS, something is still going to be a hardware bottleneck.

So don't try to eliminate bottlenecks so much as create the right experience. Finding the bottleneck is an important process if your performance is lackluster. If FPS minimums are already acceptable, it could lead you to waste money.

By the sound of it you're looking into it because you have a performance gap over where you'd like it to be. However, there are people who post with analyses like this and finding a bottleneck that upgrading to eliminate is about as beneficial as buying your computer a box of chocolates for Valentines day.

Have fun with Rome2. I've bought Rome:TW twice now and played it for hundreds of hours. Hope you are having as much fun with Rome2. I'll play it eventually, like a year from now when it's <$20 on Steam.

 

[Concillian]

It's like Steam read this post or something.

25 minutes after I made this post, I got an email from Steam saying a game on my wishlist is on sale... Rome2 for $30. Still gonna wait but... creepy.