a_c_r_e_a_l wrote: ↑13 Sep 2022, 14:46
I think it's not worth of 0.06ms and 7 FPS
Depends on the machine -- it can be a much bigger difference (or not). Also, the Hz you use, and what you're doing.
There are times where it is clumped together, e.g. weird microfreezes between refresh cycles, that adds mouse jitter or keyboard inputread jitter, etc. Affecting lagfeel.
Compositing sometimes interrupts the GPU asynchronous rendering workflow on certain GPUs, the bunching-effect that occurs, especially if you've enabled RTSS Scanline Sync, whereupon its Force Flush setting also forces the compositing operations to also complete, before the GPU can render the next frame. Ending up requiring more GPU% headroom in order to successfully maintain RTSS Scanline Sync, if DWM is turned on.
Sometimes an inefficiently (bogged-down by flaws/badly written driver hook/etc) DWM creates microstutters. Most of the time the compositing overheads is 0.1ms or less on modern fast-memory-bandwidth GPUs (0.06) especially modern RTX GPUs, but sometimes it spikes to, say, 1ms -- big enough to create human visible microstutter in strobed modes.
The top-spec RTX 4090 is rumored to do 1 terabyte per second on its memory, and compositing framebuffers (megabytes) is just child's play with that nuclear powered damburst of memory bandwidth. DWM on/off probably be virtually zero human perceivable difference, if no other overheads are bogging down. But coding in Microsoft kernel has sometimes (ahem) has been a problem. Oh and the drivers cesspool?
But in the real world, not everyone will get 4090s, drivers can be bad, OS can be bad, and 3rd party software adds processing-expensive hooks (RTSS, Alt+Z GeForce menu, RGB utilities, etc), and all those calls between Ring 0 (kernel) and userspace is expensive. Who knows, some sheninigians may move them to DPC (Deferred Procedure Calls), which can have domino effects on latencies.
As we hit 500Hz and 1000Hz, all those compositing overheads adds up. So a thousand 0.1ms translates to 100ms, a 10% slowdown in framerate during 1000Hz Microsoft Windows.
Most of the time, DWM and non-DWM makes negligible difference in most use cases, especially casual play, especially with some pros (Alt+Tabbing) sometimes exceeding the cons.
But there are exceptions where DWM "unexpectedly" add 5-10% overheads (e.g. certain ultrahighHz scanline sync algorithms on a certain brand of GPU on a certain machine). However, when Microsoft introduced the Full Screen Optimizations, things became a bit different, and sometimes overheads that didn't exist appeared, and other overheads that existed disappeared.
It's crapshoot per-machine per-GPU per-settings, but if you're ultrahigh Hz (390Hz, 500Hz, etc), it's worth at least doublechecking DWM compositing is not a major % of your system workload. I've seen it as a 0.1% workload and I've seen it as a 10% workload.
All this is just mostly academic if you have a modern GPU with fast memory. Bigger issue if integrated GPU sharing DRAM -- that's when DWM compositing gives you a bigger hit due to less memory bandwidth.
But I'm always interested in more tests of Windows 11, to see what "problems" it might have.
TL;DR: Test it out, verify it's not a major workload difference, and also doublecheck for existence of frametime spikes.