>> Hi, all >> >> The VM will get stuck for a while(about 6s for a VM with 20GB memory) when attaching a pass-through PCI card to the non-pass-through VM for the first time. >> The reason is that the host will build the whole VT-d GPA->HPA DMAR >> page-table, which needs a lot of time, and during this time, the >> qemu_global_mutex lock is hold by the main-thread, if the vcpu thread IOCTL return, it will be blocked to waiting main-thread to release the qemu_global_mutex lock, so the VM got stuck. >> The race between qemu-main-thread and vcpu-thread is shown as below, >> >> QEMU-main-thread vcpu-thread >> | | >> qemu_mutex_lock_iothread qemu_mutex_lock(&qemu_global_mutex) >> | | >> +----loop- ->+ +----loop---->+ >> | | | | >> | qemu_mutex_unlock_iothread | qemu_mutex_unlock_iothread >> | | | | >> | poll | kvm_vcpu_ioctl(KVM_RUN) >> | | | | >> | qemu_mutex_lock_iothread | | >> | | | | >> -------------------------------------------------------------------------------------- >> | | | qemu_mutex_lock_iothread >> | kvm_device_pci_assign | | >> | | | blocked to waiting main-thread to release the qemu lock >> | about 6 sec for 20GB memory | | >> | | | | >> +------------+ +-------------+ >> >> >> Any advises? >> >> Thanks, >> Zhang Haoyu > >What if you detach and re-attach? >Is it fast then? Yes, because the VT-d GPA->HPA DMAR page-table has been built, no need to re-build it. >If yes this means the issue is COW breaking that occurs with get_user_pages, not translation as such. >Try hugepages with prealloc - does it help? Yes, a bit help gained, but it cannot resolve the problem completely, the stuck still happened. Thanks, Zhang Haoyu -- 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
