On Thu, Nov 29, 2012 at 04:55:48PM +0200, Michael S. Tsirkin wrote: > On Thu, Nov 29, 2012 at 03:45:55PM +0100, Stefan Hajnoczi wrote: > > On Thu, Nov 29, 2012 at 03:12:35PM +0200, Michael S. Tsirkin wrote: > > > On Thu, Nov 22, 2012 at 04:16:52PM +0100, Stefan Hajnoczi wrote: > > > > The virtio-blk-data-plane feature is easy to integrate into > > > > hw/virtio-blk.c. The data plane can be started and stopped similar to > > > > vhost-net. > > > > > > > > Users can take advantage of the virtio-blk-data-plane feature using the > > > > new -device virtio-blk-pci,x-data-plane=on property. > > > > > > > > The x-data-plane name was chosen because at this stage the feature is > > > > experimental and likely to see changes in the future. > > > > > > > > If the VM configuration does not support virtio-blk-data-plane an error > > > > message is printed. Although we could fall back to regular virtio-blk, > > > > I prefer the explicit approach since it prompts the user to fix their > > > > configuration if they want the performance benefit of > > > > virtio-blk-data-plane. > > > > > > Not only that, this affects features exposed to guest so it really can't > > > be > > > trasparent. > > > > > > Which reminds me - shouldn't some features be turned off? > > > For example, VIRTIO_BLK_F_SCSI? > > > > Yes, virtio-blk-data-plane only starts when you give -device > > virtio-blk-pci,scsi=off,x-data-plane=on. If you use scsi=on an error > > message is printed. > > > > > > Limitations: > > > > * Only format=raw is supported > > > > * Live migration is not supported > > > > > > This is probably fixable long term? > > > > Absolutely. There are two parts: > > > > 1. Marking written memory dirty so live RAM migration can work. Missing > > today, easy cheat is to switch off virtio-blk-data-plane and silently > > switch to regular virtio-blk emulation while memory dirty logging is > > enabled. The more long-term solution is to actually communicate the > > dirty information back to the memory API. > > > > 2. Synchronizing virtio-blk-data-plane vring state with virtio-blk so > > save/load works. This should be relatively straightforward. > > > > I don't want to gate this patch series on live migration support but it > > is on my TODO list for virtio-blk-data-plane after this initial series > > has been merged. > > > > > > * Block jobs, hot unplug, and other operations fail with -EBUSY > > > > > > Hmm I don't see code to disable PCU unplug in this patch. > > > I expected no_hotplug to be set. > > > Where is it? > > > > It uses the bdrv_in_use() mechanism. > > Hmm but PCI device can still go away if > guest ejects it. Does this work fine?
Any comment?
