Hi Emanuele, On Wed, Mar 29, 2023 at 11:58:24AM +0200, Emanuele Rocca wrote: > some arm64 hosts unfortunately do not have KVM support: > > kvm [1]: HYP mode not available > > On those systems, running qemu with -cpu=cortex-a57 results in > significantly improved performance compared to -cpu=max. > > For example: here is how long it takes debvm-run to reach the point > where the hostname is being set when using -cpu=max: > > [ 34.838074] systemd[1]: Hostname set to <testvm>. > > Modifying /usr/bin/debvm-run to set CPU=cortex-a57 instead: > > [ 12.450115] systemd[1]: Hostname set to <testvm>.
Thanks for the report. Since I mainly use it on amd64, I am not affected by this change and seek feedback from Arnd and Johannes as they will be affected. My initial reaction is that I am slightly opposed to changing this, because architectures tend to bump baselines and at some point arm64 will likely have a baseline that is not met by cortex-a57. So the max value poses less maintenance cost on my side. Now this is two arguments (performance vs maintenance) and we need to strike a good balance. > Please consider using CPU=cortex-a57 instead of CPU=max for arm64, > and/or adding a command line switch to override the value of CPU. Are you aware that any options passed after a double dash are forwarded to qemu? Are you also aware that when you pass -cpu twice, the last -cpu wins? So overriding is as simple as appending "-- --cpu=cortex-a57" to your debvm-run invocation. Helmut
