View Full Version : Bottleneck Detection - help me work it out!

28-02-2013, 08:46 PM
I finally got around to buying the new NFS: Most Wanted - I'm a driving game nut so it was inevitable but I knew I'd probably run into performance issues and I have - bigstyle - I'd say it borders on unplayable tbh (tho when it's working, I rather like it)

Min Spec is
Processor: 2 GHz Dual Core (Core 2 Duo 2.4 GHZ or Atlhon X2 2.7 GHz)
Memory: 2 GB
Graphics Card (AMD): DirectX 10.1 compatible with 512 MB RAM (ATI RADEON 3000, 4000, 5000 OR 6000 series, with ATI RADEON 3870 or higher performance)
Graphics Card (NVIDIA): DirectX 10.0 compatible with 512 MB RAM (NVIDIA GEFORCE 8, 9, 200, 300, 400 OR 500 series with NVIDIA GEFORCE 8800 GT or higher performance)

Rec Spec is
Processor: Quad-Core CPU
Memory: 4 GB
Graphics Card: DirectX 11 compatible with 1024 MB RAM (NVIDIA GEFORCE GTX 560 or ATI RADEON 6950)

I have
Processor: Dual Core 2.9Ghz AMD Athlon II (Regor 245)
Memory: 4GB
Graphics Card: DirectX 11 512Mb RAM AMD 5670

So I'm below Rec. Spec. but I reckon well inside Min. Spec. - and I seriously doubt the game would be playable on their Min. Spec.

Looking around the Net, it does seem that it's just a stinker of a port - people with systems WAY beyond mine are complaining about FPS drops which are annoying to them but borderline unplayable for me (they go from 60s to 40s - I go from 30s to single figures!!)

So I thought I'd do a bit of work to try to figure-out what was causing it - I reckoned-on 4 possible explanations.

CPU-bound. Easy enough to check, just monitor CPU usage whilst played with the stock Windows Resource Monitor

GPU-bound. GPU usage is a bit harder to determine but MSI Afterburner gives a decent 'usage percentage' and will graph it over time/against FPS.

Memory-limited. The way I check for Memory 'abuse' is to monitor swapfile activity, which you can do in the Windows Resource Monitor 'Disk' panel.

HDD limited. Again we can check this in the Windows Resource Monitor.

So I went an! did all of that and y'know what? It's none of those things!

Defragging helped a BIT but there are still savage FPS drops even with the drive completely defragged.

Killing everything other than the game helped a bit (reducing swap activity/freeing memory of course) but there are still savage FPS drops

CPU usage is in the high 80s/low 90s - by comparison NFS: The Run used to peak upto 100 and that would accompany it's stuttering wheras this actually DROPS CPU usage when it's stuttering!!

GPU usage is mostly in the 70s and again falls-off rather than spiking up! I have turned-off every possible fancy graphical thing so that's not a big surprise - switching a few back on pushes that up a but but there are STILL big FPS drops. Even if I drop the game into a silly-low resolution like 1024x768 it's still stuttering.

Disc activity is OK too - closing all other programs eliminated most of the swapfile activity and with the game on a different drive to the OS (and the swapfile on another drive again) I STILL get big FPS drops!?!?

At this point I give-up - the problem has to be an optimisation problem of some sort surely because it's not using CPU, GPU or HDD and there's memory to spare so - erm - what is it doing!?

I am, however, open to any ideas - advancing the cause of bottleneck detection and all that!!

28-02-2013, 09:21 PM
It can still be CPU-limited even when CPU usage is below 100%. That's if the game is unable to make full use of the number of cores available.

01-03-2013, 01:27 AM
That wouldn't make CPU usage DROP when the game is slowing down - it would rise :)

When I saw the CPU (and GPU) drop-off around the FPS slowdowns, I assumed it was an Memory or HDD issue. The game was either loading textures/models and/or it was contending with other HDD access (e.g. swapfile or whatever), but HDD usage doesn't follow the 'slowdowns' either, it's a bit spiky most of the time and no more or less spiky when the game is struggling.

I suspect the game is simply getting tangled-up loading models and textures - it's a big city and there's an ambitious amount of models and textures being handled. Races/events are less prone to this - given that the game knows which way you're going and limits models (less traffic etc.) that would tie-up.

Some folks have pinned-down certain areas of the city which are particularly bad for slowdown and in one case my PC simply freezes for periods as I drive through an underpass (same spot EVERY time).

One of the cheekier Min Specs I've seen - some games don't run well below Rec. Spec but I've not seen one which doesn't really run AT ALL :)

Chalk 1 more mark for a new PC then :)

01-03-2013, 01:07 PM
That wouldn't make CPU usage DROP when the game is slowing down - it would rise :)

Not necessarily. If one thread is bottlenecking the game, increased demands on that thread will slow the game down, reducing the load on other threads since less is going on.

Though it's quite possible that there's something else going on. I'd be more cocksure if your CPU utilization was always hovering at some suspicious number, like 50%.

01-03-2013, 02:12 PM
Reading around, the consensus seems to be that the game bogs-down in certain locations whilst loading/processing stuff - it seems the same locations affect everyone, regardless of their rig spec, which suggests the game's problems are internal and not something we can fix for ourselves.

Amusingly, the slowdowns in singleplayer are just stutterfests which resolve themselves - but playing online, the game has to "keep you up" with everyone so any slowdown is followed by moments of CRAZY 'warp drive like' acceleration, which given the anarchic nature of it's multiplayer (aka the crashfest) is actually quite amusing :)

I can't do much else really - I normally run this PC in stock/quiet and cool setting but I tried a mild overclock (2.9->3.2) and it made no difference whatsoever - I have the OS/Swap/Game on 3 separate HDDS and I've NOTHING else running so it has over 3Gb of RAM to play with and it still bogs-down in the same places.

I'm not sure if I'd be more annoyed if I had a monster spec PC and it was chugging or not :)

Hey ho