On Thu, Dec 07, 2017 at 04:53:59PM +0000, Peter Maydell wrote: > On 7 December 2017 at 16:48, Igor Mammedov <imamm...@redhat.com> wrote: > > On Thu, 7 Dec 2017 16:05:50 +0000 > > Peter Maydell <peter.mayd...@linaro.org> wrote: > > > >> Hi; I'm currently writing '-cpu max' support for ARM. For that I'd > >> like to be able to do the "probe host kernel for its supported feature > >> set" in the CPU object's instance-init function, but I'd like to do
I don't think instance_init is appropriate for that, as object_free(object_new(t)) must be always safe to call and free of side-effects for all types. Wouldn't it work if you do that on realize? > >> it just once and cache the answer. Can I rely on something or other > >> having the BQL or otherwise ensuring that two threads don't run > >> the instance_init method in parallel (eg in a hotplug situation), > >> or do I need to create and use my own mutex to protect the cached > >> answer data? > > considering cached data shouldn't change during qemu lifetime it > > shouldn't be possible for instance_init() to clash at hotplug > > time as object_new(cpu) calls serialized within monitor/qmp loop. > > Right, that was my question -- are we guaranteed that anything > that calls object_new(cpu) does it with a lock? object_new() itself doesn't seem to be thread-safe (see type_initialize()), so I'm pretty sure there shouldn't be any object_new() calls in QEMU without the BQL being held. > > > But why cpu's instance_init, we could cache host's value at > > configure_accelerator() time (could be different depending on accel). > > I don't know if I need the information at configure_accelerator() > time (if you say "-cpu cortex-a57" then we don't need to bother > probing). The first time I know if we want to probe is when a > "-cpu host" CPU is created. > > thanks > -- PMM -- Eduardo
