On Wed, Mar 14, 2012 at 9:22 AM, Avi Kivity <avi@xxxxxxxxxx> wrote: > On 03/13/2012 12:42 PM, Amos Kong wrote: >> Boot up guest with 232 virtio-blk disk, qemu will abort for fail to >> allocate ioeventfd. This patchset changes kvm_has_many_ioeventfds(), >> and check if available ioeventfd exists. If not, virtio-pci will >> fallback to userspace, and don't use ioeventfd for io notification. > > How about an alternative way of solving this, within the memory core: > trap those writes in qemu and write to the ioeventfd yourself. This way > ioeventfds work even without kvm: > > > core: create eventfd > core: install handler for memory address that writes to ioeventfd > kvm (optional): install kernel handler for ioeventfd > > even if the third step fails, the ioeventfd still works, it's just slower. That approach will penalize guests with large numbers of disks - they see an extra switch to vcpu thread instead of kvm.ko -> iothread. It seems okay provided we can solve the limit in the kernel once and for all by introducing a more dynamic data structure for in-kernel devices. That way future kernels will never hit an arbitrary limit below their file descriptor rlimit. Is there some reason why kvm.ko must use a fixed size array? Would it be possible to use a tree (maybe with a cache for recent lookups)? Stefan -- 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
