On Tue, Feb 18, 2014 at 02:38:40AM +0000, Zhanghaoyu (A) wrote: > 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? 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? -- MST -- 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
