General CPU bottlenecking question

[rob4001]

I was wondering how old generation wise would a CPU have to before it started bottlenecking a modern GPU for example an rx480 or a 1060?

I was thinking about this for a second hand build with a decent modern gpu for current gen gaming.

So I was thinking may a q6600 can be had quite cheap..but maybe it's too old now or possibly and i5 750?

Also how do you identify bottlenecking?

[AETAaAS]

This is possibly one of the most contentious questions you can ask a forum full of tech nerds.

I would say there is no definite age where a CPU starts bottlenecking the rest of the system, it depends on the type of load and how CPU intensive it is. A fair few members here have older CPUs going with newer GPUs simply because the need for CPU power hasn't tracked evenly with graphics advances, and with ever increasing workloads in gaming being offloaded to the GPU, this may continue to be the case.

Now, how to determine bottlenecking is difficult, because there are so many different things in the background that even I/O can skew the numbers. Obviously if your CPU is pegged to 100% use then that is quite suspect if your GPU is relaxed (I used to use MSI afterburner to check this, might still be a useful tool).

[EndlessWaves]

The only definite answer is application specific, any sort of more general answer is subjective because the actual question you're asking is 'Does the CPU bottleneck enough applications to make it worth replacing?'

There are certainly modern games where a Q6600 won't bottleneck a fast card, for example:


But if you look at the rest of the article you'll find many things are limited:
http://www.techspot.com/article/1039...red/page5.html
http://www.techspot.com/article/1313...ter/page2.html

In your situation I'd probably say a Sandy Bridge i3 would be the minimum. At £80 for a complete system it doesn't really make any sense to save £20-30 for a Q6600 machine when you're spending over two hundred quid on a graphics card. Possibly even a Sandy Bridge i5 as they often go for ~£30 more.

[infraction]

I see a lot of people recommending 775 socket cpu's in youtube vids and such for budget builds which in my opinion would of been a great idea 5 years ago but now days you can find budget cpu's that offer better performance, for example the new kaby lake pentiums only cost around £60 yet they pretty much wipe the floor against most older gen i3's and even some non k i5's. And with AMD while ryzen is just around the corner their current FM2+ athlons perform substantially better than the q6600, userbenchmark shows an average effective speed of 88% over the q6600 while that is not effectively real world performance it gives you a clear idea that the q6600 has long past it's sell by date.

The 1156 socket on the other hand is still relevant though, that i5 750 is a really strong chip along with the BCLK overclocking freedom you get on a p55 motherboard it should have no trouble with most games. You might see some slight bottlenecking with the £200+ cards though but nothing too major. You could also pick up a xeon x3440 for much the same price as the i5 750 which is not too different from a first gen i7 and can be overclocked.

There is a big risk going with second hand components that old though, obviously you have no warranty as well as the fact the components might have spent the last 7-8 years being severely overclocked or in a not well cleaned system. You probably pay a bit more getting a brand new budget kaby lake build or something similar, but when you consider the performance vs risk & price it's probably safer to have a warranty for your parts and pay that little bit more if the performance is going to be roughly the same for gaming.

[kalniel]

Also how do you identify bottlenecking?

You change a load factor and observe whether it has an effect on performance.

IE, increasing the rendered resolution of a game should put more load on the GPU alone, so if the GPU is bottlenecking (the usual scenario) then you'd expect the performance to decrease. However if another component, eg CPU, is a bottleneck the performance won't change. Or vice versa - drop the resolution and you should see an increase if frame rates if the GPU is bottlenecking.

Instead of changing load factors, you can also change component speeds and see if that affects frame rate - if you change the speed and it has no effect then it wasn't a bottleneck.

Looking at load time (ie 100% cpu load) doesn't help determine bottlenecks unfortunately, especially in gaming where threading is not always very effective.

[Dashers]

I upgraded from a i7-920 to a i7-5930K as it was due, but honestly, the 920 (albeit overclocked) wasn't being taxed with gaming. Makes more sense to sink your money into GPU updates.

[scaryjim]

There's another consideration with bottlenecking, of course, which is whether the bottleneck is sufficient to impact on your real world playing experience.

Here's a hypothetical: let's suppose on one particular game an RX480 + Core i7 7700k will turn in 120fps at max settings. You swap the i7 for a Q6600, and the framerate drops to 60fps. Now, there's a clear CPU bottleneck there - but does it matter? You're still getting 60fps, which is perfectly playable.

And for a final wildcard consideration - DX12 is starting to proliferate, and is meant to help reduce CPU overhead. So as more games take advantage of DX12 fully, we could even see CPU requires fall for many games.

It's an interesting question, to which there's no easy answer. The only way to be sure would be to test all the software you want to use on systems with both new and old processors, to see what difference it made...!

[Dashers]

I think DX12 will in reality make things more CPU dependent as developers get better at parallel workflows, more work will be done on multi-core CPUs - especially the big multiplayer games.

And that's another point worth making, games like Planetside with their terrible engine design are massively CPU bound. Even a small overclock can make a noticeable difference in framerates (because, even in this day and age, somebody thought it was a good idea to wait for all other things to be processed before rendering frames).