On Thu, Apr 05, 2018 at 03:47:28PM +0000, Wang, Wei W wrote: > On Thursday, April 5, 2018 10:04 PM, Michael S. Tsirkin wrote: > > On Thu, Apr 05, 2018 at 02:05:03AM +0000, Wang, Wei W wrote: > > > On Thursday, April 5, 2018 9:12 AM, Michael S. Tsirkin wrote: > > > > On Thu, Apr 05, 2018 at 12:30:27AM +0000, Wang, Wei W wrote: > > > > > On Wednesday, April 4, 2018 10:08 PM, Michael S. Tsirkin wrote: > > > > > > On Wed, Apr 04, 2018 at 10:07:51AM +0800, Wei Wang wrote: > > > > > > > On 04/04/2018 02:47 AM, Michael S. Tsirkin wrote: > > > > > > > > On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote: > > > > > I'm afraid the driver couldn't be aware if the added hints are > > > > > stale or not, > > > > > > > > > > > > No - I mean that driver has code that compares two values and stops > > > > reporting. Can one of the values be stale? > > > > > > The driver compares "vb->cmd_id_use != vb->cmd_id_received" to decide > > > if it needs to stop reporting hints, and cmd_id_received is what the > > > driver reads from host (host notifies the driver to read for the > > > latest value). If host sends a new cmd id, it will notify the guest to > > > read again. I'm not sure how that could be a stale cmd id (or maybe I > > > misunderstood your point here?) > > > > > > Best, > > > Wei > > > > The comparison is done in one thread, the update in another one. > > I think this isn't something that could be solved by adding a lock, > unless host waits for the driver's ACK about finishing the update > (this is not agreed in the QEMU part discussion). > > Actually virtio_balloon has F_IOMMU_PLATFORM disabled, maybe we don't > need to worry about that using DMA api case (we only have gpa added to > the vq, and having some entries stay in the vq seems fine). For this > feature, I think it would not work with F_IOMMU enabled either. Adding a code comment explaining all this might be a good idea. > If there is any further need (I couldn't think of a need so far), I > think we could consider to let host inject a vq interrupt at some > point, and then the driver handler can do the virtqueue_get_buf work. > > Best, > Wei
