On 13/08/19 02:55, Wanpeng Li wrote: >> I think KVM_HINTS_REALTIME is being abused somewhat. >> It has no clear meaning and used in different locations >> for different purposes. > > Now it disables pv queued spinlock, pv tlb shootdown, pv sched yield > which are not expected present in vCPUs are never preempted for an > unlimited time scenario.
Guest side polling definitely matches the purpose of KVM_HINTS_REALTIME. While host-side polling is conditional on single_task_running, this is obviously not true of guest-side polling. The alternative would be to enable it only if KVM_FEATURE_POLL_CONTROL is available, but I prefer Wanpeng's patch. Paolo >> For example, i think that using pv queued spinlocks and >> haltpoll is a desired scenario, which the patch below disallows. > > So even if dedicated pCPU is available, pv queued spinlocks should > still be chose if something like vhost-kthreads are used instead of > DPDK/vhost-user. kvm adaptive halt-polling will compete with > vhost-kthreads, however, poll in guest unaware other runnable tasks in > the host which will defeat vhost-kthreads. > > Regards, > Wanpeng Li >
