On Fri, Nov 05, 2021 at 10:35:20 +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. The above is all wrong after the refactors. > 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. > > Resolves: https://gitlab.com/libvirt/libvirt/-/issues/229 > Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx> > Tested-by: Kashyap Chamarthy <kchamart@xxxxxxxxxx> > --- > src/qemu/qemu_command.c | 5 +++ > ...efault-cpu-tcg-features.x86_64-latest.args | 40 +++++++++++++++++++ > tests/qemuxml2argvtest.c | 1 + > 3 files changed, 46 insertions(+) > create mode 100644 tests/qemuxml2argvdata/x86_64-default-cpu-tcg-features.x86_64-latest.args > > diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c > index 0257b86a0d..17ee3c5d3a 100644 > --- a/src/qemu/qemu_command.c > +++ b/src/qemu/qemu_command.c > @@ -7271,6 +7271,11 @@ qemuBuildAccelCommandLine(virCommand *cmd, > switch ((virDomainVirtType)def->virtType) { > case VIR_DOMAIN_VIRT_QEMU: > virBufferAddLit(&buf, "tcg"); > + > + if (def->features[VIR_DOMAIN_FEATURE_TCG] == VIR_TRISTATE_SWITCH_ON) { Similarly to previous commit. It's not extensible when adding new tcg features. This would set the cache to 0 if a new feature is added and tb-cache is not used. > + virBufferAsprintf(&buf, ",tb-size=%llu", > + def->tcg_features->tb_cache >> 10); Okay, so input in libvirt is kiB, output is MiB. This means we are truncating precision. In this case I don't think it's worth adding checks, but at least the docs should mention what's going on. > + } > break;
