* Marcelo Tosatti | 2015-04-08 20:33:23 [-0300]: >Sebastian, Hi Marcelo, >rebased against v3.18.7-rt2 as requested. > >The problem: > >On -RT, an emulated LAPIC timer instance 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. Applied, thanks. Sebastian -- 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
