Alt-Tab = low FPS

[bell_rj]

So I'm running DCS 2.5 in 'Full Screen' mode at high settings and getting stutter free results of between 60-90fps depending upon the scene and it looks superb. If I Alt+Tab out to another app and back into DCS, I find that the FPS halves and stutter begins. The game window looks the same - no borders/window chrome and it looks full screen. Apart from the low FPS/stutter, no-one would be any the wiser that I'd Alt+Tabbed in the first place.

 

If I then hit Alt+Enter (which is the Windows shortcut key for switching a window between full screen and windowed) then the expected high FPS and smooth gameplay returns instantly.

 

I see a lot of people reporting low FPS with pretty capable rigs and wondered if this issue had caught anyone out. Is anyone else seeing this issue?

[Sideslip]

So I'm running DCS 2.5 in 'Full Screen' mode at high settings and getting stutter free results of between 60-90fps depending upon the scene and it looks superb. If I Alt+Tab out to another app and back into DCS, I find that the FPS halves and stutter begins. The game window looks the same - no borders/window chrome and it looks full screen. Apart from the low FPS/stutter, no-one would be any the wiser that I'd Alt+Tabbed in the first place.

 

If I then hit Alt+Enter (which is the Windows shortcut key for switching a window between full screen and windowed) then the expected high FPS and smooth gameplay returns instantly.

 

I see a lot of people reporting low FPS with pretty capable rigs and wondered if this issue had caught anyone out. Is anyone else seeing this issue?

 

Nvidia? Gsync? Windows 10?

 

I know in EVERY game I have, not only DCS, if I alt-tab Vsync and Gsync gets wonky. Latest drivers (only updated because that problem started), seems to have started after Fall Creator's Update but not sure.

 

- If Vsync is set to on in Nvidia Control Pannel (NCP) and I tab out and back, it will still be synced but it is now using "fast sync" (unlimited fps with no tearing, can tell by perfect micro stutter once per second when limited to 99/100fps or 101/100fps but not 100/100)

 

- If Vsync is on in DCS (and NCP) then when I alt-tab again vsync is still on, but is now stuck at half-refresh (50fps in my case)

 

- If I am using Gsync set to "full screen only", the same thing happens as above but I no longer have Gsync.

 

- If I am using Gsync set to "fullscreen and windowed" then Gsync continues to work as before... however, about 50% of the time DCS would drop to 25fps with 8% and 10% CPU and GPU usage respectively (unless it is in the background, then it runs normally). This does not happen in all games, but it does in a few.

 

- In games that allow changing of settings on the fly, enabling and disabling Vsync seems to reset everything back to normal without the need to restart the program.

 

This all applies to DCS 1.5, but considering it happens in everything I have it's safe to say it will happen in 2.5.

 

As you notice the stutter after coming back in, if you have a Gsync monitor that would explain it as you will certainly notice the difference from the loss. If you use Vsync and are normally capped at the monitor refresh rate, again that would explain the stutter due to the change to fast sync (from exceeding the refresh).

 

If I Alt+Tab out to another app and back into DCS, I find that the FPS halves and stutter begins.

 

Make sure Vsync is disabled in DCS and that shouldn't happen (as much). You are being forced into double buffered Vsync which means if you can't get your monitor's refresh rate 100% of the time, it will keep you at half-refresh. Note that it is not only DCS, as I get the same behavior with the Heaven 4.0 benchmark program as well. Make sure everything you run has Vsync off in it's settings and use NCP to turn it on. At least that way if you alt-tab you won't have low fps (but you will get some micro-stutter unless you use a frame limiter like RivaTuner).

[Sideslip]

Another thing I suspect is that the reason using alt-enter to get your framerate back after alt-tabbing is that switching out of DCS puts it in windowed mode and upon returning to the game it stays that way. Hitting alt-enter simply puts it back to full screen. Upon returning to fullscreen vsync goes back to normal (still at the loss of G-sync in my case). It's odd that this also switches it back to normal vsync from the fast sync it was using in windowed mode if G-sync was not used. And again using G-sync in "fullscreen and windowed" seems to avoid this problem, though it may be staying in windowed mode with G-Sync disabled, which seems to be unavoidable in any case.

 

I don't know if it is the same way for you, but when I alt-tab DCS remains visible in front of the desktop, that's why I think it is switched to windowed-fullscreen.

Edited February 3, 2018 by Sideslip

[Sideslip]

You can also try the latest Nvidia driver if you are running a 1080, but as far as I can tell it doesn't fix anything. At least not in DCS. FPS still skyrockets to 200 when I tab out even though it should be restricted to 100 and it doesn't seem like Gsync turns back on when returning.

 

Edit: Actually I take back that last part about Gsync not turning back on with the new drivers. After further testing it is hard to conclude either way, but at least in the Heaven Benchmark it seems to re-enable it's self. However, the wonky Vsync is still there.

 

https://www.geforce.com/drivers/results/130633

 

Changes and Fixed Issues in Version 390.77

The following sections list the important changes and the most common issues resolved in this version. This list is only a subset of the total number of changes made in this

driver version. The NVIDIA bug number is provided for reference.

 

Fixed Issues in this Release

 

[sLI][Dirt 4]: There is corruption and flickering in the game with SLI enabled.

[200376552]

 

[Neverwinter Nights]: Some graphics are missing. [2024453]

 

[Optimus Notebook]: GeForce Experience may launch with a black screen. [2009290]

 

[3DMark]: There is a drop in the benchmark performance. [2042217]

 

[GeForce GTX 1080][G-SYNC]: Performance issues occurred with G-SYNC windowed mode enabled. [2032623]

 

[GeForce GTX 1070 Ti][NVIDIA Control Panel]: The NVIDIA Control Panel->Output

Dynamic Range setting does not persist but switches from Full to Limited after

rebooting the system. [200378878]

Edited February 3, 2018 by Sideslip

[bell_rj]

Thnaks Sideslip for your detailed replies. I am using G-Sync with an Nvidia 1070ti on Windows 10 and I also have V-Sync enabled in the DCS options. I'm fairly new to G-Sync so not too familar with fast sync so thank you for your explanation. I think you are correct in your analysis and when I alt-tab DCS does stay in front of the desktop. If, for exmample, I need to change my HOTAS profile through a taskbar icon I have to force the start menu and taskbar to the foreground.

 

I will try disabling v-sync as you suggest and setting the Nvidia g-sync setting to full screen only and see what happens then.

[monkie]

Thank you so much for explaining the whole full window V-synch/G-synch thing Sideslip.

 

 

I went back in and disabled V-synch in game as well as turning off MSAA. In Nvidia Control Panel I selected V-synch as well as G-synch on. Also turned on AA via NCP.

 

 

Entered game and saw my frames were not stable and then Alt-Enter one time and they went to steady 60FPS and the performance was an amazing smooth vs what I was seeing before. I am guessing my G-synch is properly working at this point.

 

 

Thanks that was driving me crazy before.

[BitMaster]

I alt-tabbed in n out of DCS last night without any glitch while on VA-Srv.

 

I am using the newest 390.77 driver for 2 days now ( good mining drive as a side note ).

 

You might want to try that driver and check again.

[Sideslip]

I will try disabling v-sync as you suggest and setting the Nvidia g-sync setting to full screen only and see what happens then.

 

You can still use vsync if you like, just only through the NCP and keep it off through in-game settings. Also to get the task bar visible after alt-tab you can just hit the "windows key" and it should pop up.

[Sideslip]

So I've been smashing my head against the wall with DCS trying to get Gsync to work properly. I've finally 100% confirmed to have it working.

 

As such I am also able to confirm that at least in my case with 390.77 drivers and a 1080 that if you alt-tab out of DCS, when you go back Gsync will not be working. But if you do the alt-enter thing as bell_rj originally suggested, it will start working again. Very odd considering I'm using the "windowed and fullscreen" option for Gsync.

 

I've also 100% confirmed that if DCS is not set to run in full screen (unchecked in settings) Gsync will not be working. As soon as you alt-enter to full screen it will work again. Maybe it's a problem on ED's end but knowing Nvidia and Microsoft drivers... I don't think so. 2 steps forward and 1 step back should be their motto.

 

Also, my monitor display's "Gsync Mode" in it's on-screen display but that doesn't mean it's actually working. All it means is that it's enabled. You have to use the Mk1 eyeball to test it (or possibly 3rd party programs).

[BitMaster]

...........ehhhhhh, that might explain something I experienced today. ! Thank you.

 

My monitor has a red LED when in Gsync, white or amber when not, but maybe it is as you say and Gsync can get disabled and I had my "nahh, this doesnt feel likew always" experience andf thought its because I tried 4x msaa and def shaders, maybe it was Gsync being off... i actually dont know know what caused it and msaa may not be to blame but Gsync.

[Sideslip]

More digging...

 

So I used "Nvidia Profile Inspector" to see what was in the DCS profile and, well, I guess I found what I suspected all along. Gsync in DCS is set to "fullscreen only" no matter what you set in NCP. If I look at PUBG it shows "windowed and fullscreen".

 

DCS Profile:

 

PUBG Profile:

 

I can however force Gsync to windowed mode using the profile inspector and Gsync will then indeed work when DCS is windowed or after alt-tabbing without switching back to full screen (I know for sure because the PG348Q flickers at the top 1 inch of the screen when the framerate is bouncing between Gsync and Vsync, usually caused by stuttering and doesn't happen with Gsync-off). The problem is DCS stutters horribly in windowed mode like this and even though Gsync is working, it looks terrible. Switching back to fullscreen instantly makes it smooth again.

 

So just to recap all these posts:

 

- Vsync is wonky with Nvidia when alt-tabbing any games, so be careful

 

- Vsync must always be disabled in-game if you are using Gsync (mostly to avoid being stuck at half-refresh when windowed). If you want to use Vsync (I personally do) you must only enable it in NCP

 

- When alt-tabbing, DCS will switch to and remain in windowed mode

 

- DCS can be toggled between windowed and fullscreen with alt-enter (you definitely want to do this after tabbing back)

 

- Gsync will not run in windowed mode with DCS unless you use "Nvidia Profile Inspector" to force it manually. NCP does not work, it will only allow fullscreen Gsync

 

- DCS runs like crap with Gsync in windowed mode, so if you want Gsync you should always make sure it is fullscreen. This is however in 1.5.8, but unless there is some miracle with 2.5 I would think it is the same.

 

- If you have a GTX1080 and run Gsync in "windowed and fullscreen" you probably should update to the 390.77 drivers as it should have fixed the "I'm getting 25fps and 10% GPU usage" bug.

Edited February 4, 2018 by Sideslip