Comment 0 for bug 1988527

On Power9 the qemu based autopkgtest commands create VMs that are extremely slow and fail with obscure errors (partially discussed in LP: #1973628, comment 8). This can be reproduced for example by running:

  autopkgtest-buildvm-ubuntu-cloud -v -r jammy --ram-size 1024

but autopkgtest-virt-qemu is also affected. The extreme slowness of the VMs made me think that something was off with the virtualization settings. I modified autopkgtest_qemu.py so that qemu-system-ppc64le is called with '-machine accel=kvm' (which I think is the same as '-machine pseries,accel=kvm' with pseries being the default machine type).

With this change everything is very fast and reliable. These warnings also went away:

qemu-system-ppc64le: warning: TCG doesn't support requested feature, cap-cfpc=workaround
qemu-system-ppc64le: warning: TCG doesn't support requested feature, cap-sbbc=workaround
qemu-system-ppc64le: warning: TCG doesn't support requested feature, cap-ibs=workaround
qemu-system-ppc64le: warning: TCG doesn't support requested feature, cap-ccf-assist=on

indicating that we were using TCG emulation before.

I imagine that Qemu has good reasons not to default to accel=kvm or accel=kvm:tcg on ppc64, but think it's reasonable to assume it's available and enable it in autopkgtest.

We can fix this in autopkgtest upstream, but it would be nice to verify if this is an issue with Debian too before submitting a salsa MR.

[1] https://wiki.qemu.org/Documentation/TCG