On Thu, Nov 04, 2021 at 01:22:53PM +0100, Michal Privoznik wrote: > Alright, here's the deal: to enable tb-cache one has to use > '-accel tcg,tb-size=' which then conflicts with '-machine > accel=tcg'. But sure, we can use the old -accel in this specific > case. But because of how the tb-size argument is defined in QEMU > there's no way for us to have a capability check. The feature was > introduced in QEMU commit of v5.0.0-rc0~175^2~62 and is tied to > TCG only. Therefore, I think we can live without capability > check. Worst case scenario, QEMU fails to start. Hmm, you write: "... we can use the old -accel", I was told by Paolo Bonzini the other day that "-accel" is preferred instead of "-machine accel". Hence I filed this GitLab ticket a couple of days: https://gitlab.com/libvirt/libvirt/-/issues/233 (Use `-accel` instead of `-machine accel`) [...] -- /kashyap