On 11/25/2014 12:21 PM, Marcelo Tosatti wrote: > The problem: > > On -RT, an emulated LAPIC timer instances has the following path: > > 1) hard interrupt > 2) ksoftirqd is scheduled > 3) ksoftirqd wakes up vcpu thread > 4) vcpu thread is scheduled > > This extra context switch introduces unnecessary latency in the > LAPIC path for a KVM guest. > > The solution: > > Allow waking up vcpu thread from hardirq context, > thus avoiding the need for ksoftirqd to be scheduled. > > Normal waitqueues make use of spinlocks, which on -RT > are sleepable locks. Therefore, waking up a waitqueue > waiter involves locking a sleeping lock, which > is not allowed from hard interrupt context. > What are the consequences for the realtime kernel of making waitqueue traversal non-preemptible? Is waitqueue traversal something that ever takes so long we need to care about it being non-preemptible? -- 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
