At 45:35 Alex addresses this, but there are several parts of the explanation that I don't follow. If I've understood correctly, he's stating that the 30 FPS V-Sync mode provided on the Steam Deck is a form of linear/first-in-first-out V-Sync where the additional input lag comes from those extra queued frames whereas when you're not using the 30 FPS V-Sync mode the system uses "Fast Sync" style Triple Buffering. Here's where they lost me though -- capping the framerate in conjunction with V-Sync is a proven method of reducing input lag on PC (see the BlurBuster's Low Lag V-Sync Guide or test it yourself by enabling V-Sync in a title with no FPS cap then versus with an RTSS cap set at 60 on a 60 hz panel for example). Capping the framerate very clearly reduces input delay with traditional V-Sync modes (if I had to guess "why" probably because you're filling the V-Sync back-buffer "just in time"). This is also the case with 30 FPS -- e.g. Half-Refresh V-Sync ON + a 30 FPS cap will yield lower input lag results than only turning Half-Refresh V-Sync ON with no FPS cap. I have tested this many times myself across different machines where my conclusion is that the "optimal" approach to traditional V-Sync is something like (assuming the target is 30 on a 60 hz screen): 1) Half-Refresh V-Sync ON 2) Cap the framerate to True Refresh/2 (you may need to tinker a bit though as if you cap too low the back buffer isn't filled in time and you can get stutters) 3) Keep the CPU prerender queue in check to prevent latency from that coming into play I've listened that segment of their video like 3 times and it "sounds like" Alex is describing the input lag difference between Fast Sync Style Triple Buffering and FIFO/linear style triple buffering, but isn't that not the question? (Or, have I misunderstood the question -- my bet is I've just missed something here). I thought the question was whether the method of limiting the framerate used by the Steam Deck itself adds delay, not the V-Sync method. It almost sounds like he's suggesting that the 30 fps cap simply enables half-refresh rate tripled buffered v-sync while not actually imposing an RTSS style cap at all, but I think I'm just misunderstanding what he's saying. It also sounds like he's saying the Steam Deck basically always runs in windows mode and when V-Sync is OFF it automatically enables Fast Sync style triple buffering (though I'm still in the dark on whether he meant this is what the system does just with standard v-sync on and the 30 fps cap not in play). If any of you could clear this up for me, that'd be awesome -- I really just am not sure I followed his meaning correctly here. Thanks,
Someone on the video in the comments replied to me and said that enabling an engine limiter of 30 to be on top of whatever the steam deck is doing noticeably reduced delay so I wonder if it’s just applying triple buffered half refresh Vsync without an actual fps limit of 30 to go atop that. Not sure as I don’t have one to test myself so I’m also not clear on exactly what steam’s UI suggests these settings do.
