On 9 October 2018 at 15:23, Daniel P. Berrangé <berra...@redhat.com> wrote: > On Tue, Oct 09, 2018 at 02:58:41PM +0100, Peter Maydell wrote: >> On 9 October 2018 at 14:43, Cornelia Huck <coh...@redhat.com> wrote: >> > I'm not sure why a single accelerator (any of them) would be a good >> > default. A list (tcg:kvm:<whatever>) sounds much saner, as it would >> > continue to work even if some accelerators have been disabled (right?) >> > >> > (And I'd prefer kvm to be first in that list; anything that relies on >> > tcg being used should specify it explicitly... a normal user will >> > likely always want the fast variant.) >> >> tcg should be the default for binaries without KVM compiled in, >> of course... But as Thomas points out, the reason for our current >> default is the usual "because we tend not to change things that >> would break existing working command lines". > > Putting KVM first shouldn't break existing working command lines > in general.
There are ARM QEMU command lines which will fail with KVM and work with TCG (eg ones which use -cpu something-other-than-host or which ask for a GICv3 when the host has only a GICv2). These are basically cases where KVM can't provide features that TCG can. I imagine other archs like power have similar. thanks -- PMM
