On 06/03/20 11:20, David Hildenbrand wrote: > Yeah, rwlocks are not optimal and I am still looking for better > alternatives (suggestions welcome :) ). Using RCU might not work, > because the rcu_read region might be too big (esp. while in KVM_RUN). > > I had a prototype which used a bunch of atomics + qemu_cond_wait. But it > was quite elaborate and buggy. > > (I assume only going into KVM_RUN is really affected, and I do wonder if > it will be noticeable at all. Doing an ioctl is always already an > expensive operation.) > > I can look into per-cpu locks instead of the rwlock. Assuming we're only talking about CPU ioctls (seems like a good approximation) maybe you could use start_exclusive/end_exclusive? The current_cpu->in_exclusive_context assignments can be made conditional on "if (current_cpu)". However that means you have to drop the BQL, see process_queued_cpu_work. It may be a problem. Paolo
