Multi GPU Thoughts - Micro Stuttering Redux

[Final8y]

First I would like to mention that it is not the first time that someone brings problems with Multi GPU implementations into the spotlight, as you may already have heard about "micro stuttering". Micro stuttering was described as an uneven frame rate when using two GPUs, something that may happen for other reasons like lack of RAM, software accessing the HDD at the same time, software using the CPU(s), etc. Many things can disturb frame rate but the issue with micro stuttering was that the uneven frame rate seemed to only occur when SLI or CrossFire are in use. PCGH had a look at the problems and published some data a while back and it was an interesting look at the problem. The issue is that they didn't notice the problem's origin. They noticed that frames were arriving at uneven intervals, which mitigates the purpose of a higher frame rate providing better responsiveness, which is what is expected from these setups. Keep this in mind: better frame rate must be equal to better responsiveness, or it's a moot point.
Still, an uneven interval should still provide better responsiveness nonetheless, if the frame rate is going to almost 2x. This is where it gets tricky: looking at just the frame times doesn't show you the real problem that's going on with contemporary multi GPU solutions, the big problem is that the responsiveness is in fact worse!

Before we dwell any further into this issue, we need to look at multi GPU rendering modes and have a more detailed look at how the issue presents itself to the user.

http://www.siliconmadness.com/2011/09/multi-gpu-thoughts-micro-stuttering.html

 

[Final8y]

I have not read it closely at all but some of what he is using is way past its sell by date.

Also i keep seeing the 30fps bench and really most people would be upgrading if they were getting an average of 30fps in multi GPU in most of their games.

 

[Final8y]

Yeah gotta agree there - unfortunatly multi GPU does not work well if your having to resort to it just to get 30fps... where multi GPU is at its best is when you use it to ensure you get as high as possible minimum fps and as close to 60fps (or higher) as possible - multi GPU with low end cards rarely makes sense... mid-range solutions sometimes where its cost effective and one card produces "ok" performance.

Indeed.

 

[Final8y]

From the article:



The whole point of the setup was to allow us to see the effect in action - this is only possible around the 30fps mark - beyond that all you get is the 'feels unresponsive' - which is difficult to quantify.

It is a fascinating read (worth it guys - not just a skim...) - effectively he has concluded that AFR is a compromise that is not working and the manufacturers need to look again to find a better solution, rather than just relying on faster frame rates to mask the issue.

The only bit I thought was weak was the OS issue he identified - Server 2008 had none of the uneven frame-rate issues which everyone assumes is responsible for micro-stuttering, yet even there the ghosting is apparent. Either the uneven rate isn't responsible for the stutter, or the ghosting is caused by another, unidentified, issue - this side definitely needs more investigation.

Everything is a compromise at some level.
Maybe we should have all set our CRT monitors to 30Hz just so we can say how CRT was a compromise of showing motion.

But i don't get any off the issues he has as he is using very old SLi 9400 GT.