our downstream virt folks have started to do some more testing of different confguration
and on differnet acrchitecutres and it appears that 32 is not a good default.
on arch64 values over 24 prevent the guest form properly booting and intial indication
are that the memory use while initally low ~0.7m per port grows after the the guest os intiallies the pci device as such it looks like defaultign to 32 or 24 would cause excessive memory usage to be a sane default.
initial testing a sweet spot in terms of memory overhead may be 16 ports or less.
after the guest fully initializes the devices the overhead grows form about 0.7M per device to ~4M per device based on the average useage over 15 spawns of an instance but the deleta betwen 4 pcie ports and 16 is within 1 sandard devation.
our downstream virt folks have started to do some more testing of different confguration
and on differnet acrchitecutres and it appears that 32 is not a good default.
on arch64 values over 24 prevent the guest form properly booting and intial indication
are that the memory use while initally low ~0.7m per port grows after the the guest os intiallies the pci device as such it looks like defaultign to 32 or 24 would cause excessive memory usage to be a sane default.
initial testing a sweet spot in terms of memory overhead may be 16 ports or less.
after the guest fully initializes the devices the overhead grows form about 0.7M per device to ~4M per device based on the average useage over 15 spawns of an instance but the deleta betwen 4 pcie ports and 16 is within 1 sandard devation.
this testing was done by dan berrangé using libvirt directly with
the following setup.
- a Fedora 30 host
- qemu 3.1.0
- libvirt 5.1.0
- A Fedora 28 x86_64 guest OS
- 2000 MB of RAM allocated
- 8 vCPUs, freely floating
- Memory set to preallocated, and locked in physical RAM
- One disk, as an qcow2 overlay on a master readonly f28 image
- One network PCI device
- One video PCI device
- One memory balloon PCI device
- VNC graphics, no client connected
graph or data todate /berrange. fedorapeople. org/q35- usage.png
https:/
note the yellow line uses the second y axis on the right
were as the magenta and blue axis use the y axis on the left.