On 01/03/2011 11:46 AM, Jan Kiszka wrote:
Hi, at least in kvm mode, the qemu_fair_mutex seems to have lost its function of balancing qemu_global_mutex access between the io-thread and vcpus. It's now only taken by the latter, isn't it? This and the fact that qemu-kvm does not use this kind of lock made me wonder what its role is and if it is still relevant in practice. I'd like to unify the execution models of qemu-kvm and qemu, and this lock is the most obvious difference (there are surely more subtle ones as well...).
IIRC it was used for tcg, which has a problem that kvm doesn't have: a tcg vcpu needs to hold qemu_mutex when it runs, which means there will always be contention on qemu_mutex. In the absence of fairness, the tcg thread could dominate qemu_mutex and starve the iothread.
This doesn't happen with kvm since kvm vcpus drop qemu_mutex when running. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
