the real impacts here are the userland/kernel space barrier.

Games, for instance; don't cross that boundary as much as, say, networked databases.

What about qemu with virtio networking and drives?

Then yes, very much impacted.

Yeah, aren’t most games single-threaded? I doubt this affects gaming performance very much.

Games have necessarily become more and more parallelised (whether through multithreading or multiprocessing) over the last decade, as even consoles are multi-core these days.

Both XB1 and PS4 have 8 cores (2xJaguar modules). Both also reserve one of the core exclusively for the system, so a single-threaded game would only leverage 14% of available CPU compute power.

The Switch is somewhat similar through to a lower extent: it effectively uses a quad-core ARM, with one of the core reserved to the system leaving 3 to game developers.

Most games are heavily multithreaded.

For the last decade most of them are console ports, consoles have many CPU cores since Xbox 360 (3 cores / 6 threads, 2005) and PS3 (1+6 asymmetric cores, 2006).

Most games render from single thread, but besides submitting these draw calls games do a lot of things under the hood.

When running Overwatch under VFIO according to Task Manager and i7z tool on the host it loads cores pretty evenly for me.

Can't keep 150 FPS at all times during a replay for instance, gonna disable mitigations and see if anything changes.

EDIT: nothing drastic happened, probably need to disable Windows protections as well.

Can't edit anymore, so adding here. Between 'not vulnerable' and 'max speed' there are a few different intermediate states, probably was in one of those. And I have to admit that for All Green in spectre-meltdown-checker.sh and InSpectre.exe I'd have to pay a pretty noticeable price based on my Overwatch VFIO testing.

Pretty sure there's no point returning to that intermediate state again, might as well commit to one or the other.