On Tue, 9 Feb 2016 12:48:42 +0100 <[email protected]> wrote: > Hi all i want to ask if UEFI/OVMF based VM provide some benefits as Legacy > BIOS based VM is there less IRQ, more performance or something else? > > I still use legacy bios based machine.
The VGA space itself is a shared resource, so every time the guest tries to access VGA space it gets gets trapped into QEMU, which forwards the request to VFIO, which negotiates with the VGA arbiter and adjusts chipset routing as necessary. Therefore VGA mode is bearable when there's one consumer, once you start getting contention and the arbiter needs to switch routing on each access, this can certainly become a bottleneck. However, even when using a legacy BIOS with x-vga, those VGA accesses *only* occur during early boot or if you're using non-accelerated drivers, so the window for contention is very small. Once the guest is up and running, access to legacy VGA space ceases, and there's no performance difference between legacy BIOS and UEFI that I'm aware of. FWIW, it's also a misconception that Q35 based VMs provide some sort of performance advantage vs 440FX. The chipset is virtual, it has no bearing on performance. Thanks, Alex _______________________________________________ vfio-users mailing list [email protected] https://www.redhat.com/mailman/listinfo/vfio-users
