On Wed, Jul 31, 2024 at 08:30:46AM GMT, Markus Armbruster wrote: > I apologize for the delay. > > Daniel Henrique Barboza <dbarb...@ventanamicro.com> writes: > > > We're not honouring KVM options that are provided by any -accel option > > aside from the first. In this example: > > > > qemu-system-riscv64 -accel kvm,riscv-aia=emul (...) \ > > -accel kvm,riscv-aia=hwaccel > > > > 'riscv-aia' will be set to 'emul', ignoring the last occurrence of the > > option that set 'riscv-aia' to 'hwaccel'. > > The way you phrase this, it sounds like a bug. But as far as I know, > -accel is meant to have fallback semantics: we use the first one that > works.
The fact that some (most?) parameters have override semantics and some have fallback semantics makes our complicated command line even more complicated, especially since there's no way to know which is which. IMHO, always having override semantics and then providing new parameters, e.g. -accel-fallback (or a property, -accel fallback=on,...), would go a long way to bringing some order to the universe. > > Perhaps: > > -accel has fallback semantics, i.e. we try accelerators in order until > we find one that works. Any remainder is ignored. > > Because of that, you can't override properties like this: > > qemu-system-riscv64 -accel kvm,riscv-aia=emul (...) \ > -accel kvm,riscv-aia=hwaccel > > When KVM is available, 'riscv-aia' will be set to 'emul', and the > second -accel is ignored. When KVM is not available, neither option > works, and the command fails. > > Why would you want to override accelerator properties? Testing. Many properties are only available to allow the user to force non defaults. The example above isn't exactly what triggered this. The real use is, '-accel kvm' is the default used by libvirt and when riscv-aia=hwaccel is possible, it will default to hwaccel. In order to test riscv-aia emulation support using libvirt (which doesn't yet allow selecting anything riscv specific), I attempted to use the qemu commandline element to override -accel with kvm,riscv-aia=emul. Thanks, drew
