Hi, Currently in virtio host dictates the size and layout of vq that should be used. To talk to a device that has one vq with 128 elements guest needs to allocate at least 2 pages. Usually this is not a problem, but sometimes guest runs in a resource restricted environment and then it may not have enough memory to initialize all virtio devices present in the system. One such environment is a BIOS. Seabios currently has virtio block support. Since the BIOS should be able to access the disk even after OS is launched vq should be allocated from a special memory region that will be marked as unavailable to an OS, but such memory is scarce. Because vq is so huge only a couple of virtio disks can be initialized by the BIOS. It would be nice if a guest will be able to tell to a host what vq size should be used instead. BIOS issues only one request at a time anyway, so it needs only one element in vq. It does not care about performance to much either, so it can tell to a host to not align used index to a page boundary. This way vq of one element shouldn't take more then a couple hundreds of bytes. -- Gleb. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
