On 09/27/2012 11:11 AM, Gleb Natapov wrote: >> >> User return notifier is per-cpu, not per-task. There is a new task_work >> (<linux/task_work.h>) that does what you want. With these >> technicalities out of the way, I think it's the wrong idea. If a vcpu >> thread is in userspace, that doesn't mean it's preempted, there's no >> point in boosting it if it's already running. >> > Ah, so you want to set bit in kvm->preempted_vcpus if task is _not_ > TASK_RUNNING in sched_out (you wrote opposite in your email)? If a task > is in userspace it is definitely not preempted. No, as I originally wrote. If it's TASK_RUNNING when it saw sched_out, then it is preempted (i.e. runnable), not sleeping on some waitqueue, voluntarily (HLT) or involuntarily (page fault). > >> btw, we can have secondary effects. A vcpu can be waiting for a lock in >> the host kernel, or for a host page fault. There's no point in boosting >> anything for that. Or a vcpu in userspace can be waiting for a lock >> that is held by another thread, which has been preempted. > Do you mean userspace spinlock? Because otherwise task that's waits on > a kernel lock will sleep in the kernel. I meant a kernel mutex. vcpu 0: take guest spinlock vcpu 0: vmexit vcpu 0: spin_lock(some_lock) vcpu 1: take same guest spinlock vcpu 1: PLE vmexit vcpu 1: wtf? Waiting on a host kernel spinlock is not too bad because we expect to be out shortly. Waiting on a host kernel mutex can be a lot worse. -- 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
