On 07/01/2020 15.37, Paolo Bonzini wrote: > On 07/01/20 14:55, Christophe de Dinechin wrote: >> So what about ranking the accelerators, so that all combinaisons >> -accel=kvm:tcg, -accel=tcg:kvm, -accel kvm -accel tcg, etc would > > (I assume you mean "-machine accel=kvm:tcg" and "-machine accel=tcg:kvm" > for the first two. This is the "older" way which has now become sugar > for "-accel kvm -accel tcg"). > >> all pickup kvm if available, and tcg as a fallback? Implementation-wise, >> it would simply mean ranking the accelerators and updating the accelerator >> only if it’s available and better. > > This is an interesting idea. I like this better than "-accel best", > because "-accel best" has the problem that you can't add suboptions to > it (the suboptions for the various accelerators are disjoint). > > It would break backwards compatibility for "-machine accel=tcg:kvm", > which so far meant "use TCG if compiled in, otherwise use KVM". This is > not something I would have a problem with... except that "tcg:kvm" is > the default if no -accel option is provided!
Note that we need "-M accel=tcg:kvm" (or "-accel tcg -accel kvm" now) in tests/boot-serial-test.c for example, since some machines can't use KVM on certain hosts (e.g. with KVM-HV on POWER8/9). Thomas
