FreeSync + VSync = DeadSync

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JambyStrikesAgain
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FreeSync + VSync = DeadSync

Post by JambyStrikesAgain »

I recently upgraded my PC to a 5800X paired with 16GB DDR4@3600 (mainly cause of my new 200+ hours world that reached the peak my old 3550k).
Got no problem at all on first playthrough of couple hours after that upgrade.

The next start of the game (couple of days later), however, was way worse. FPS are down to 1-2, even in the main menu. That happened without me changing almost anything; I just had set the right XMP profile for my memory taking them to a timing of 18,22,22,42@3600, and slightly (-0.1V) down-volted the CPU in order to keep temperatures a little lower, but I don't think that should have any impact on FPS. By chance Factorio got updated to 1.1.32 but I checked with previous version and the issue is the same.

After some investigation I discovered that the only way to get back to the 60/60 is to disable VSync, disable full-screen, or disable FreeSync on my main Samsung U28E590D. I admit I have no idea how VSync should be set if FreeSync is enabled, but It seems odd that the combo completely kills FPS.
Moreover, I have never changed VSync, FreeSync or any GPU settings prior to the appearance of the problem. I have played with this GPU (still a R9 280) and this monitor since at least January, when I got the new monitor; had no issue at all, tough my old CPU could not keep 60 UPS in my main world.

Any idea on how that could have happened, and what config should I prefer? Empirically it seems to me that disabling VSync makes FPS wobbling a bit on 59.9-60FPS, while disabling FreeSync keeps them locked at 60FPS, at least for the in-game counter.

cbhj1
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Re: FreeSync + VSync = DeadSync

Post by cbhj1 »

That combination of settings sounds like a deadlock, the monitor waiting on the video update and the video update waiting on the monitor refresh.

could your video drivers have been updated automatically?

JambyStrikesAgain
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Re: FreeSync + VSync = DeadSync

Post by JambyStrikesAgain »

cbhj1 wrote:
Tue Apr 20, 2021 10:23 pm
That combination of settings sounds like a deadlock, the monitor waiting on the video update and the video update waiting on the monitor refresh.

could your video drivers have been updated automatically?
I have checked, and indeed AMD Display drivers got update to 27.20.21001.7005 about a week ago by Windows Update; not entirely sure it was in between my runs, but most probably yes. It feels weird that an update can totally destroy the playability of a configuration, thought I guess I could try downgrading them or just stick with VSync off.

san
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Re: FreeSync + VSync = DeadSync

Post by san »

I am not sure if the latest Windows Update KB5001330 is to blame as well https://www.windowslatest.com/2021/04/1 ... lure-bsod/

Zanthra
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Re: FreeSync + VSync = DeadSync

Post by Zanthra »

Freesync on with VSync off will be a fine configuration unless you notice screen tearing.

I don't know the details on Freesync but if it works similar to GSync, VSync only matters if the buffer flip happens while the GPU is already sending frame data to the display. With VSync enabled, it will finish submitting the current frame, and submit the new frame for the next available refresh time. With VSync disabled, it will immediately change the data being sent to the display, potentially causing screen tearing. At any other time, the monitor holds the previous frame on screen and the interface is free for the next frame that is rendered (within certain limits to keep hardware mouse cursor movement reasonable in very flow FPS situations). This allows the frame to be submitted immediately on the buffer flip, making screen tearing unlikely even without VSync.

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