On Mon, Aug 4, 2014 at 6:21 PM, Stefan Hajnoczi <stefa...@redhat.com> wrote: > On Fri, Aug 01, 2014 at 03:42:05PM +0800, Ming Lei wrote: >> On Thu, Jul 31, 2014 at 5:18 PM, Paolo Bonzini <pbonz...@redhat.com> wrote: >> > Il 31/07/2014 05:22, Ming Lei ha scritto: >> >>> > >> >>> > The problem is that g_slice here is not using the slab-style allocator >> >>> > because the object is larger than roughly 500 bytes. One solution >> >>> > would >> >>> > be to make virtqueue_pop/vring_pop allocate a VirtQueueElement of the >> >>> > right size (and virtqueue_push/vring_push free it), as mentioned in the >> >>> > review of patch 8. >> >> Unluckily both iovec and addr array can't be fitted into 500 bytes, :-( >> >> Not mention all users of VirtQueueElement need to be changed too, >> >> I hate to make that work involved in this patchset, :-) >> > >> > Well, the point of dataplane was not just to get maximum iops. It was >> > also to provide guidance in the work necessary to improve the code and >> > get maximum iops without special-casing everything. This can be a lot >> > of work indeed. >> > >> >>> > >> >>> > However, I now remembered that VirtQueueElement is a mess because it's >> >>> > serialized directly into the migration state. :( So you basically >> >>> > cannot change it without mucking with migration. Please leave out >> >>> > patch >> >>> > 8 for now. >> >> save_device code serializes elem in this way: >> >> >> >> qemu_put_buffer(f, (unsigned char *)&req->elem, >> >> sizeof(VirtQueueElement)); >> >> >> >> so I am wondering why this patch may break migration. >> > >> > Because you change the on-wire format and break migration from 2.1 to >> > 2.2. Sorry, I wasn't clear enough. >> >> That is really a mess, but in future we still may convert VirtQueueElement >> into a smart one, and keep the original structure only for save/load, but >> a conversion between the two structures is required in save/load. > > This is a good idea. The VirtQueueElement structure isn't complicated, > it's just big. Just use the current layout as the serialization format.
The patch shouldn't be complicated too, and the only annoying part is to find each virtio device's load/save , and add the conversion in the two functions if VirtQueueElement is involved. I suggest to do the conversion in another standalone patchset. Thanks,
