Locking Frame Rate

[Zimmerbz 153]

I'm not very technical nor do I have a poor performing sim, but I was curious what does locking the frame rates do in the P3d settings opposed to having them unlimited (this is what I have it set to).  I fly PMDG/FSLabs (V4.1) and have lots of payware airports along with Orbx Open LC and Base.  I get smooth performance with an occasional hiccup when I dense airport comes into view.  However, it is nothing to get frustrated with.  I was just curious as to what I should have that setting to if having it at unlimited might be an issue at some point.  When checking fps, I have seen it as low as 20 and as high as 50 depending on the situation so I wasn't sure if that was because I had it on unlimited and I could be benefiting if I set it somewhere in the middle.  Thanks

[SteveW 1,792]

Setting an fps lock with the slider control in P3D display settings determines the time between frames. The simulated physics, the location of the plane and scenery is all determined by the fixed time between frames making it accurate. The way it does this is by making the frames ahead of time so that with any hiccups in the flow the next frame is already available to display on time. There are usually three look-ahead frames ready to fill-in where the sim slows down. To be sure there is always enough frames to fill-in when the time comes, there must be adequate performance overhead for the sim to create the extra frames as we fly. Any flutter in the sim flow could deplete the look-ahead frames and when the sim is stressed it has no time to replenish them. Locked is very hard on the sim, we need to see double the desired fps with slider set to Unlimited and VSync=Off before locking at half that.

When we use the VSync=On setting with Unlimited set on the slider, this uses the monitor refresh frequency to determine the nominal time between frames but each frame takes a different time to build. This makes the flow inconsistent even though it appears to be at or about the monitor refresh frequency it has a hard job to keep it even.

When we set the Triple Buffer=On with VSync=On and Unlimited on the slider this helps with the time between frames for the simulated physics, the location of the plane and scenery similar to locked fps, just not quite as accurate but it does not help with the apparent flow to the display.

[Zimmerbz 153]

So given that I am set at unlimited with vsync on, should I be doing anything differently?  I don't notice any lags or anything besides an occasional slow autogen popping up when changing views or a little slow load time / stutter when approaching a high detail airport.  However, the "issues" aren't a bother to me since for the most part I am smooth.  

[SteveW 1,792]

No you should be OK with VSync=On & Unlimited. Check the refresh frequency of the monitor. Say it is 60Hz for argument sake (updates per second) - the sim will try to make 60 frames per second. If the sim can maintain 60fps or more it will appear smooth, when the sim can't make 60fps you see the inconsistent flow. If trying the Locked setting, you could try 7,10,15,20 or 30 Locked with the 60Hz monitor increasing the co-incidence of frame to refresh timing with those fps settings on that monitor. However since the Locked fps setting creates look ahead frames it would often be doing more work at 30 Locked than VSync at 60.

Generally I bring settings down a bit so that there is overhead in the system to up its game when the going gets rough.

[IAhawkeyeDDS 158]

in my anecdotal testing my system performs best (with a 4K g-sync monitor but g-sync turned off) set to unlimited frames and vsync=off.  I usually get ~ 20-30 fps landing in Chicago (either FSDT-KORD or flyTampa-KMDW) --> and typically I'll get about 4 occurrences of a long stop that will last ~ 4 seconds and then continue onward.  The 'long stops' don't bother me all that much an I attribute them to both KMDW and KORD loading as I pan around.  Also using MT6 set at 17% commercial traffic. 

When I lock FPS at 24 then my approaches drop to around 6-10 fps - but no 'long stops'.

I'm fairly un-knowledgable when it comes to hardware stuff but this is just what I've noticed.  So I'll take the occasional 'long stop' as the sim runs much smoother at unlimited FPS.  BTW this testing was done with PMDG 737 and typical cruise FPS is between 40-60 fps in the VC and outside view can be up around 80 FPS.

[Cruachan 705]

Hi Steve,

Forgive me if I dare to interject with what may seem to be some muddled thinking...or not as the case may be...lol 

I have experimented with this a lot in the past and found eventually that the most consistent fluidity of performance was achieved on my rig by employing VSync ON, Frame rate locked at 31fps (in-sim) and Monitor refresh fixed at 120Hz. G-Sync is OFF while P3D is running.

If I'm honest, the reason why this should be so is not entirely clear. I prefer a frame rate lock as it is much easier on the GPU and reserves some useful overhead for those occasions when the sim is entering denser areas of scenery. With VSync ON, and the observable fact that my customised sim installation rarely manages to maintain or exceed 60fps (let alone 120) using an unlimited setting, the frame rate is dropped down to the next best max of 30fps (120/4), yet I find that performance also remains pretty fluid with VSync OFF and without changing the in-sim frame rate lock of 31fps. Running Unlimited, with or without VSync, is generally unacceptable as I start to see micro stuttering even at relatively high frame rates. Locking at 31fps seems to guarantee a frame rate at or very close to 30fps, most of the time, and this is reflected on how well the sim performs 😀

How am I doing?

Regards,

Mike 🤓

 

[SteveW 1,792]

With VSync=Off and Unlimited on the fps Slider each next frame comes after the last, the average time between frames is used as the physics time, so in effect the frame displayed is never in the correct place.

All the frames made above the refresh frequency are ignored. Since there is no hunting around the VSync frequency there is no 'sawtooth' to the flow around that frequency, it is super stable at the monitor frequency so long as it can be maintained.

[Tony P 160]

My 2 cents... set VSYNC & TB on with Unlimited and then set your monitor refresh to 30Hz.  Amazingly smooth performance. 

Try it!

[SteveW 1,792]

1 minute ago, Tony P said:

My 2 cents... set VSYNC & TB on with Unlimited and then set your monitor refresh to 30Hz.  Amazingly smooth performance. 

Try it!

Yes that would be a good setup. 30 locked would require more PC power.

In the end anything from 30fps or above is going to be pretty good because there's little time between frames and what's required is consistent time between frames or we can see it.

[David Roch 1,953]

Hi Steve,
Do you mind having a look at this thread?
Maybe can you point me to any direction to sort out this issue with unlimited frames?
Thanks in advance.

[Zimmerbz 153]

4 minutes ago, SteveW said:

Yes that would be a good setup. 30 locked would require more PC power.

In the end anything from 30fps or above is going to be pretty good because there's little time between frames and what's required is consistent time between frames or we can see it.

What is TB?  Pardon my ignorance!

[SteveW 1,792]

11 minutes ago, Cruachan said:

Hi Steve,

Forgive me if I dare to interject with what may seem to be some muddled thinking...or not as the case may be...lol 

I have experimented with this a lot in the past and found eventually that the most consistent fluidity of performance was achieved on my rig by employing VSync ON, Frame rate locked at 31fps (in-sim) and Monitor refresh fixed at 120Hz. G-Sync is OFF while P3D is running.

If I'm honest, the reason why this should be so is not entirely clear. I prefer a frame rate lock as it is much easier on the GPU and reserves some useful overhead for those occasions when the sim is entering denser areas of scenery. With VSync ON, and the observable fact that my customised sim installation rarely manages to maintain or exceed 60fps (let alone 120) using an unlimited setting, the frame rate is dropped down to the next best max of 30fps (120/4), yet I find that performance also remains pretty fluid with VSync OFF and without changing the in-sim frame rate lock of 31fps. Running Unlimited, with or without VSync, is generally unacceptable as I start to see micro stuttering even at relatively high frame rates. Locking at 31fps seems to guarantee a frame rate at or very close to 30fps, most of the time, and this is reflected on how well the sim performs 😀

How am I doing?

Regards,

Mike 🤓

 

Seems good Mike! That's basically what we have to do - try it all out. Everyone is different what they want so it's down to personal preference which compromises we make.

[Zimmerbz 153]

And where do you set the monitor refresh rate?  Is that in a monitor setting or in the sim?

[SteveW 1,792]

7 minutes ago, Zimmerbz said:

What is TB?  Pardon my ignorance!

The triple buffer is a technique in the GPU that uses a third frame buffer so that when one frame is being displayed and the backbuffer has ended drawing, the third buffer can begin drawing the next frame, physics calculated at a more consistent time between frames. It's a technique that is used with Unlimited and VSync=On so doesn't improve the smoothness of frames displayed, just the location shown in the view.

[Zimmerbz 153]

9 minutes ago, SteveW said:

The triple buffer is a technique in the GPU that uses a third frame buffer so that when one frame is being displayed and the backbuffer has ended drawing, the third buffer can begin drawing the next frame, physics calculated at a more consistent time between frames. It's a technique that is used with Unlimited and VSync=On so doesn't improve the smoothness of frames displayed, just the location shown in the view.

Is TB something that I need to turn on or is it automatically done when Unlimited and Vsync is on?