3 ms·
>may have performance advantages in some situations s/may/certainly s/some/almost all It's not a small gap, either. You are basically doubling the number of c
by cthalupa 11y ago
>may have performance advantages in some situations
s/may/certainly
s/some/almost all
It's not a small gap, either. You are basically doubling the number of context switches required for system calls with PV, due to AMD removing CPU protection rings from x86_64, forcing this separation to have to happen in software. You lose out on EPT, so your page table performance suffers in almost all workloads. You cannot take advantage of SR-IOV for NICs or nvme.
PVH might be an answer someday, but for now, there is a pretty massive performance loss. Context switches are important. Memory latency is important. (Nearly) direct access to the hardware is important.
- lsc 11y agoI'm not saying you are wrong about performance (other than to point out that actually using the qemu devices is even slower.) Still, if you go through the xsa list, if I was running HVM, I'd have had to reboot pretty often. It's a huge firedrill every time the security list sends something out, for those of us who use (normally lower-stress) local disk. Twice in one year is bad enough.
- cthalupa 11y agoWell, yeah, software emulated hardware is slow, but no one should be using emulated PCI devices on anything. There are PV or better yet, SR-IOV drivers that can be used for those that are going to be the closest to bare metal performance you'll get in a VM.