Slow to display Tianocore Bios with large amounts of RAM

[Marshalleq]

I'm aware a few of us have this issue - where it takes a very long time to boot and longer when you have more memory.  I've just seen something that I thought I'd share.

 

Basically, while watching HTOP, starting a VM that isn't already started with dedicated (not shared / ballooned) 32GB RAM, the VIRT Ram is set straight away to 32GB, but the RES RAM slowly counts up to 32GB.  Once the RES RAM reaches 32GB, suddenly the TIANOCORE BIOS is displayed and then we're good to get booting.

 

While the VM is active, reboots etc are performed normally, i.e. not slow, it's just the first boot from power on.

 

So my uneducated guess is that it takes time for KVM to find available RAM that may have been virtually assigned to other processes and make it available to the KVM / OVMF / Tianocore bios and further that the BIOS will not start until this is done.  However, with ballooned memory it also seems to need to wait to see the whole 32GB before displaying the bios.

 

Subsequent reboots continue to behave the same (bios does not come up until the RES ram in htop is completely assigned, however these subsequent reboots perform this step much faster.  I assume if one leaves the system for some time, the ram previously assigned to the VM has been used by other processes and again will be slow to assign.  I have certainly experienced that behaviour.

 

This KVM article goes some way to explain when the assigning of memory takes place within the various steps of making hardware available.

http://www.linux-kvm.org/downloads/lersek/ovmf-whitepaper-c770f8c.txt

 

This is probably a question we'd need to raise with the KVM developers.  Is anyone on that list?