Re: Qemu storage performance drops when smp > 1 (NetBSD 9.3 + Qemu/nvmm + ZVOL)

["B. Atticus Grobe" <grobe0ba%gmail.com@localhost>]

Forgive me if I've misread, but it seems like you're running 3 VMs with
2 vCPUs each on a dual-core processor. ZFS itself is also processor and RAM
heavy (on every OS I've used it on, never have used it on NetBSD).

So, it seems to me like you've taken an already not particularly fast
processor and applied a really heavy load to it, especially if you're doing
any zRAID or anything else.

Someone actually familiar with the NetBSD kernel can correct me on this,
but I'm fairly sure that the kernel itself is multithreaded, and handles
interrupts on multiple cores.

I would guess that with the single vCPU VMs, the processor was able to
keep up, but now you've doubled down on the workload, and considerably
increased the number of context switches that have to happen.

Or maybe I'm completely wrong on every point. I'd certainly take a look
at your CPU usage though.