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 >> 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? > 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
