On Friday, April 6, 2018 2:30 AM, Michael S. Tsirkin wrote: > 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. Thanks, will do. Best, Wei
